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 $188.71   3.844%   $195.964   $195.96   $195.95   $196.00  
  Purchase #2 $11.77   8.727%   $12.7972   $12.80   $12.80   $12.80  
  Purchase #3 $150.42   5.368%   $158.4945   $158.49   $158.50   $158.50  
  Purchase #4 $189.68   10.184%   $208.997   $209.00   $209.00   $209.00  
  Purchase #5 $177.75   12.339%   $199.6826   $199.68   $199.70   $199.70  
  Purchase #6 $245.39   10.202%   $270.4247   $270.42   $270.40   $270.40  
  Purchase #7 $7.43   5.636%   $7.8488   $7.85   $7.85   $7.80  
  7 purchase totals = $971.15       $1,054.2088   $1,054.20   $1,054.20   $1,054.20