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 $136.63   3.220%   $141.0295   $141.03   $141.05   $141.00  
  Purchase #2 $245.65   13.389%   $278.5401   $278.54   $278.55   $278.50  
  Purchase #3 $59.46   11.154%   $66.0922   $66.09   $66.10   $66.10  
  Purchase #4 $181.68   11.157%   $201.95   $201.95   $201.95   $202.00  
  Purchase #5 $220.85   4.544%   $230.8854   $230.89   $230.90   $230.90  
  Purchase #6 $235.51   13.727%   $267.8385   $267.84   $267.85   $267.80  
  Purchase #7 $54.53   7.825%   $58.797   $58.80   $58.80   $58.80  
  7 purchase totals = $1,134.31       $1,245.1327   $1,245.14   $1,245.20   $1,245.10