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 $57.64   12.231%   $64.6899   $64.69   $64.70   $64.70  
  Purchase #2 $207.32   9.201%   $226.3955   $226.40   $226.40   $226.40  
  Purchase #3 $197.59   10.234%   $217.8114   $217.81   $217.80   $217.80  
  Purchase #4 $64.31   4.179%   $66.9975   $67.00   $67.00   $67.00  
  Purchase #5 $184.57   5.496%   $194.714   $194.71   $194.70   $194.70  
  Purchase #6 $41.82   4.433%   $43.6739   $43.67   $43.65   $43.70  
  Purchase #7 $41.69   11.106%   $46.3201   $46.32   $46.30   $46.30  
  7 purchase totals = $794.94       $860.6023   $860.60   $860.55   $860.60