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 $66.75   4.754%   $69.9233   $69.92   $69.90   $69.90  
  Purchase #2 $212.52   10.278%   $234.3628   $234.36   $234.35   $234.40  
  Purchase #3 $45.25   9.807%   $49.6877   $49.69   $49.70   $49.70  
  Purchase #4 $88.69   4.784%   $92.9329   $92.93   $92.95   $92.90  
  Purchase #5 $157.87   11.453%   $175.9509   $175.95   $175.95   $176.00  
  Purchase #6 $84.77   11.170%   $94.2388   $94.24   $94.25   $94.20  
  Purchase #7 $211.39   3.607%   $219.0148   $219.01   $219.00   $219.00  
  7 purchase totals = $867.24       $936.1112   $936.10   $936.10   $936.10