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 $84.39   12.211%   $94.6949   $94.69   $94.70   $94.70  
  Purchase #2 $74.95   10.388%   $82.7358   $82.74   $82.75   $82.70  
  Purchase #3 $132.79   11.773%   $148.4234   $148.42   $148.40   $148.40  
  Purchase #4 $207.68   10.515%   $229.5176   $229.52   $229.50   $229.50  
  Purchase #5 $49.69   3.542%   $51.45   $51.45   $51.45   $51.50  
  Purchase #6 $8.76   12.200%   $9.8287   $9.83   $9.85   $9.80  
  Purchase #7 $52.75   9.820%   $57.9301   $57.93   $57.95   $57.90  
  7 purchase totals = $611.01       $674.5805   $674.58   $674.60   $674.50