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 $53.36   10.504%   $58.9649   $58.96   $58.95   $59.00  
  Purchase #2 $237.51   10.660%   $262.8286   $262.83   $262.85   $262.80  
  Purchase #3 $199.44   10.496%   $220.3732   $220.37   $220.35   $220.40  
  Purchase #4 $46.77   7.527%   $50.2904   $50.29   $50.30   $50.30  
  Purchase #5 $72.46   11.159%   $80.5458   $80.55   $80.55   $80.50  
  Purchase #6 $159.78   7.339%   $171.5063   $171.51   $171.50   $171.50  
  Purchase #7 $143.76   9.203%   $156.9902   $156.99   $157.00   $157.00  
  7 purchase totals = $913.08       $1,001.4994   $1,001.50   $1,001.50   $1,001.50