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 $119.67   9.464%   $130.9956   $131.00   $131.00   $131.00  
  Purchase #2 $242.68   12.473%   $272.9495   $272.95   $272.95   $272.90  
  Purchase #3 $182.63   10.167%   $201.198   $201.20   $201.20   $201.20  
  Purchase #4 $215.51   4.602%   $225.4278   $225.43   $225.45   $225.40  
  Purchase #5 $84.65   11.175%   $94.1096   $94.11   $94.10   $94.10  
  Purchase #6 $126.75   6.351%   $134.7999   $134.80   $134.80   $134.80  
  Purchase #7 $68.82   8.431%   $74.6222   $74.62   $74.60   $74.60  
  7 purchase totals = $1,040.71       $1,134.1026   $1,134.11   $1,134.10   $1,134.00