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 $58.87   5.131%   $61.8906   $61.89   $61.90   $61.90  
  Purchase #2 $202.48   4.610%   $211.8143   $211.81   $211.80   $211.80  
  Purchase #3 $98.43   4.334%   $102.696   $102.70   $102.70   $102.70  
  Purchase #4 $143.30   3.263%   $147.9759   $147.98   $148.00   $148.00  
  Purchase #5 $197.73   11.457%   $220.3839   $220.38   $220.40   $220.40  
  Purchase #6 $63.76   13.344%   $72.2681   $72.27   $72.25   $72.30  
  Purchase #7 $10.89   4.777%   $11.4102   $11.41   $11.40   $11.40  
  7 purchase totals = $775.46       $828.4390   $828.44   $828.45   $828.50