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 $184.98   4.820%   $193.896   $193.90   $193.90   $193.90  
  Purchase #2 $176.67   6.381%   $187.9433   $187.94   $187.95   $187.90  
  Purchase #3 $68.46   5.602%   $72.2951   $72.30   $72.30   $72.30  
  Purchase #4 $142.41   5.779%   $150.6399   $150.64   $150.65   $150.60  
  Purchase #5 $220.76   13.795%   $251.2138   $251.21   $251.20   $251.20  
  Purchase #6 $216.48   12.209%   $242.91   $242.91   $242.90   $242.90  
  Purchase #7 $149.89   7.382%   $160.9549   $160.95   $160.95   $161.00  
  7 purchase totals = $1,159.65       $1,259.8530   $1,259.85   $1,259.85   $1,259.80