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 $67.76   5.778%   $71.6752   $71.68   $71.70   $71.70  
  Purchase #2 $221.94   4.718%   $232.4111   $232.41   $232.40   $232.40  
  Purchase #3 $157.30   12.318%   $176.6762   $176.68   $176.70   $176.70  
  Purchase #4 $7.91   11.165%   $8.7932   $8.79   $8.80   $8.80  
  Purchase #5 $117.72   11.382%   $131.1189   $131.12   $131.10   $131.10  
  Purchase #6 $177.25   9.436%   $193.9753   $193.98   $194.00   $194.00  
  Purchase #7 $134.92   13.636%   $153.3177   $153.32   $153.30   $153.30  
  7 purchase totals = $884.80       $967.9676   $967.98   $968.00   $968.00