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 $168.49   12.147%   $188.9565   $188.96   $188.95   $189.00  
  Purchase #2 $60.75   8.788%   $66.0887   $66.09   $66.10   $66.10  
  Purchase #3 $67.50   8.820%   $73.4535   $73.45   $73.45   $73.50  
  Purchase #4 $91.36   5.783%   $96.6433   $96.64   $96.65   $96.60  
  Purchase #5 $82.48   11.462%   $91.9339   $91.93   $91.95   $91.90  
  Purchase #6 $196.29   6.763%   $209.5651   $209.57   $209.55   $209.60  
  Purchase #7 $26.87   4.615%   $28.1101   $28.11   $28.10   $28.10  
  7 purchase totals = $693.74       $754.7511   $754.75   $754.75   $754.80