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 $175.48   9.134%   $191.5083   $191.51   $191.50   $191.50  
  Purchase #2 $48.41   13.669%   $55.0272   $55.03   $55.05   $55.00  
  Purchase #3 $160.66   10.323%   $177.2449   $177.24   $177.25   $177.20  
  Purchase #4 $175.67   9.833%   $192.9436   $192.94   $192.95   $192.90  
  Purchase #5 $37.53   12.238%   $42.1229   $42.12   $42.10   $42.10  
  Purchase #6 $205.57   6.541%   $219.0163   $219.02   $219.00   $219.00  
  Purchase #7 $118.97   5.593%   $125.624   $125.62   $125.60   $125.60  
  7 purchase totals = $922.29       $1,003.4872   $1,003.48   $1,003.45   $1,003.30