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 $56.85   12.151%   $63.7578   $63.76   $63.75   $63.80  
  Purchase #2 $94.75   10.445%   $104.6466   $104.65   $104.65   $104.60  
  Purchase #3 $186.47   13.200%   $211.084   $211.08   $211.10   $211.10  
  Purchase #4 $238.26   5.354%   $251.0164   $251.02   $251.00   $251.00  
  Purchase #5 $192.66   10.712%   $213.2977   $213.30   $213.30   $213.30  
  Purchase #6 $220.96   9.307%   $241.5247   $241.52   $241.50   $241.50  
  Purchase #7 $213.83   5.225%   $225.0026   $225.00   $225.00   $225.00  
  7 purchase totals = $1,203.78       $1,310.3298   $1,310.33   $1,310.30   $1,310.30