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 $16.81   4.739%   $17.6066   $17.61   $17.60   $17.60  
  Purchase #2 $171.69   13.556%   $194.9643   $194.96   $194.95   $195.00  
  Purchase #3 $94.75   10.520%   $104.7177   $104.72   $104.70   $104.70  
  Purchase #4 $156.26   7.131%   $167.4029   $167.40   $167.40   $167.40  
  Purchase #5 $189.35   11.671%   $211.449   $211.45   $211.45   $211.40  
  Purchase #6 $75.71   6.586%   $80.6963   $80.70   $80.70   $80.70  
  Purchase #7 $174.95   9.196%   $191.0384   $191.04   $191.05   $191.00  
  7 purchase totals = $879.52       $967.8752   $967.88   $967.85   $967.80