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 $194.47   4.783%   $203.7715   $203.77   $203.75   $203.80  
  Purchase #2 $6.77   6.863%   $7.2346   $7.23   $7.25   $7.20  
  Purchase #3 $139.63   12.372%   $156.905   $156.91   $156.90   $156.90  
  Purchase #4 $206.57   10.281%   $227.8075   $227.81   $227.80   $227.80  
  Purchase #5 $168.54   5.662%   $178.0827   $178.08   $178.10   $178.10  
  Purchase #6 $138.45   12.663%   $155.9819   $155.98   $156.00   $156.00  
  Purchase #7 $33.29   6.616%   $35.4925   $35.49   $35.50   $35.50  
  7 purchase totals = $887.72       $965.2757   $965.27   $965.30   $965.30