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 $84.28   12.424%   $94.7509   $94.75   $94.75   $94.80  
  Purchase #2 $211.90   10.738%   $234.6538   $234.65   $234.65   $234.70  
  Purchase #3 $65.57   4.716%   $68.6623   $68.66   $68.65   $68.70  
  Purchase #4 $250.51   6.519%   $266.8407   $266.84   $266.85   $266.80  
  Purchase #5 $127.43   10.140%   $140.3514   $140.35   $140.35   $140.40  
  Purchase #6 $57.45   12.850%   $64.8323   $64.83   $64.85   $64.80  
  Purchase #7 $107.77   4.275%   $112.3772   $112.38   $112.40   $112.40  
  7 purchase totals = $904.91       $982.4686   $982.46   $982.50   $982.60