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 $160.92   11.113%   $178.803   $178.80   $178.80   $178.80  
  Purchase #2 $70.47   7.735%   $75.9209   $75.92   $75.90   $75.90  
  Purchase #3 $135.28   10.531%   $149.5263   $149.53   $149.55   $149.50  
  Purchase #4 $220.68   10.613%   $244.1008   $244.10   $244.10   $244.10  
  Purchase #5 $53.70   12.391%   $60.354   $60.35   $60.35   $60.40  
  Purchase #6 $195.76   5.428%   $206.3859   $206.39   $206.40   $206.40  
  Purchase #7 $184.50   7.117%   $197.6309   $197.63   $197.65   $197.60  
  7 purchase totals = $1,021.31       $1,112.7218   $1,112.72   $1,112.75   $1,112.70