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 $174.92   8.740%   $190.208   $190.21   $190.20   $190.20  
  Purchase #2 $115.28   3.773%   $119.6295   $119.63   $119.65   $119.60  
  Purchase #3 $75.48   9.370%   $82.5525   $82.55   $82.55   $82.60  
  Purchase #4 $62.40   11.442%   $69.5398   $69.54   $69.55   $69.50  
  Purchase #5 $158.28   9.164%   $172.7848   $172.78   $172.80   $172.80  
  Purchase #6 $61.67   12.763%   $69.5409   $69.54   $69.55   $69.50  
  Purchase #7 $45.46   4.628%   $47.5639   $47.56   $47.55   $47.60  
  7 purchase totals = $693.49       $751.8194   $751.81   $751.85   $751.80