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 $89.93   4.507%   $93.9831   $93.98   $94.00   $94.00  
  Purchase #2 $106.60   11.829%   $119.2097   $119.21   $119.20   $119.20  
  Purchase #3 $211.97   5.800%   $224.2643   $224.26   $224.25   $224.30  
  Purchase #4 $57.52   11.430%   $64.0945   $64.09   $64.10   $64.10  
  Purchase #5 $87.63   9.545%   $95.9943   $95.99   $96.00   $96.00  
  Purchase #6 $235.85   5.405%   $248.5977   $248.60   $248.60   $248.60  
  Purchase #7 $88.91   5.664%   $93.9459   $93.95   $93.95   $93.90  
  7 purchase totals = $878.41       $940.0895   $940.08   $940.10   $940.10