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 $32.63   5.591%   $34.4543   $34.45   $34.45   $34.50  
  Purchase #2 $201.47   10.562%   $222.7493   $222.75   $222.75   $222.70  
  Purchase #3 $245.95   4.648%   $257.3818   $257.38   $257.40   $257.40  
  Purchase #4 $225.81   12.612%   $254.2892   $254.29   $254.30   $254.30  
  Purchase #5 $55.52   10.454%   $61.3241   $61.32   $61.30   $61.30  
  Purchase #6 $73.26   8.592%   $79.5545   $79.55   $79.55   $79.60  
  Purchase #7 $212.30   11.355%   $236.4067   $236.41   $236.40   $236.40  
  7 purchase totals = $1,046.94       $1,146.1599   $1,146.15   $1,146.15   $1,146.20