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 $60.93   11.689%   $68.0521   $68.05   $68.05   $68.10  
  Purchase #2 $232.57   8.158%   $251.5431   $251.54   $251.55   $251.50  
  Purchase #3 $145.63   6.656%   $155.3231   $155.32   $155.30   $155.30  
  Purchase #4 $51.96   13.103%   $58.7683   $58.77   $58.75   $58.80  
  Purchase #5 $89.53   7.208%   $95.9833   $95.98   $96.00   $96.00  
  Purchase #6 $71.33   4.330%   $74.4186   $74.42   $74.40   $74.40  
  Purchase #7 $194.99   4.301%   $203.3765   $203.38   $203.40   $203.40  
  7 purchase totals = $846.94       $907.4650   $907.46   $907.45   $907.50