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 $224.48   6.398%   $238.8422   $238.84   $238.85   $238.80  
  Purchase #2 $68.71   10.142%   $75.6786   $75.68   $75.70   $75.70  
  Purchase #3 $164.62   12.287%   $184.8469   $184.85   $184.85   $184.80  
  Purchase #4 $149.94   12.709%   $168.9959   $169.00   $169.00   $169.00  
  Purchase #5 $139.86   12.467%   $157.2963   $157.30   $157.30   $157.30  
  Purchase #6 $69.64   5.255%   $73.2996   $73.30   $73.30   $73.30  
  Purchase #7 $236.77   6.571%   $252.3282   $252.33   $252.35   $252.30  
  7 purchase totals = $1,054.02       $1,151.2877   $1,151.30   $1,151.35   $1,151.20