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 $23.70   11.401%   $26.402   $26.40   $26.40   $26.40  
  Purchase #2 $32.65   13.817%   $37.1613   $37.16   $37.15   $37.20  
  Purchase #3 $169.70   8.508%   $184.1381   $184.14   $184.15   $184.10  
  Purchase #4 $245.98   9.428%   $269.171   $269.17   $269.15   $269.20  
  Purchase #5 $171.49   12.519%   $192.9588   $192.96   $192.95   $193.00  
  Purchase #6 $63.65   3.618%   $65.9529   $65.95   $65.95   $66.00  
  Purchase #7 $19.52   11.334%   $21.7324   $21.73   $21.75   $21.70  
  7 purchase totals = $726.69       $797.5165   $797.51   $797.50   $797.60