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 $234.99   12.317%   $263.9337   $263.93   $263.95   $263.90  
  Purchase #2 $65.99   10.599%   $72.9843   $72.98   $73.00   $73.00  
  Purchase #3 $118.68   13.211%   $134.3588   $134.36   $134.35   $134.40  
  Purchase #4 $208.88   3.121%   $215.3991   $215.40   $215.40   $215.40  
  Purchase #5 $137.42   9.622%   $150.6426   $150.64   $150.65   $150.60  
  Purchase #6 $125.56   8.476%   $136.2025   $136.20   $136.20   $136.20  
  Purchase #7 $84.32   4.339%   $87.9786   $87.98   $88.00   $88.00  
  7 purchase totals = $975.84       $1,061.4996   $1,061.49   $1,061.55   $1,061.50