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 $63.88   4.748%   $66.913   $66.91   $66.90   $66.90  
  Purchase #2 $170.56   4.136%   $177.6144   $177.61   $177.60   $177.60  
  Purchase #3 $45.94   9.627%   $50.3626   $50.36   $50.35   $50.40  
  Purchase #4 $140.60   5.177%   $147.8789   $147.88   $147.90   $147.90  
  Purchase #5 $72.48   4.351%   $75.6336   $75.63   $75.65   $75.60  
  Purchase #6 $54.69   8.618%   $59.4032   $59.40   $59.40   $59.40  
  Purchase #7 $197.68   13.338%   $224.0466   $224.05   $224.05   $224.00  
  7 purchase totals = $745.83       $801.8523   $801.84   $801.85   $801.80