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 $179.46   8.550%   $194.8038   $194.80   $194.80   $194.80  
  Purchase #2 $87.45   10.867%   $96.9532   $96.95   $96.95   $97.00  
  Purchase #3 $247.96   4.265%   $258.5355   $258.54   $258.55   $258.50  
  Purchase #4 $143.48   12.837%   $161.8985   $161.90   $161.90   $161.90  
  Purchase #5 $28.43   10.482%   $31.41   $31.41   $31.40   $31.40  
  Purchase #6 $175.89   5.842%   $186.1655   $186.17   $186.15   $186.20  
  Purchase #7 $125.47   8.390%   $135.9969   $136.00   $136.00   $136.00  
  7 purchase totals = $988.14       $1,065.7634   $1,065.77   $1,065.75   $1,065.80