Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $221.32   10.692%   $244.9835   $244.98   $245.00   $245.00  
  Purchase #2 $195.71   11.814%   $218.8312   $218.83   $218.85   $218.80  
  Purchase #3 $180.53   3.407%   $186.6807   $186.68   $186.70   $186.70  
  Purchase #4 $104.91   9.218%   $114.5806   $114.58   $114.60   $114.60  
  Purchase #5 $238.69   10.711%   $264.2561   $264.26   $264.25   $264.30  
  Purchase #6 $225.71   6.412%   $240.1825   $240.18   $240.20   $240.20  
  Purchase #7 $201.96   4.568%   $211.1855   $211.19   $211.20   $211.20  
  7 purchase totals = $1,368.83       $1,480.7001   $1,480.70   $1,480.80   $1,480.80