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 $58.59   5.677%   $61.9162   $61.92   $61.90   $61.90  
  Purchase #2 $141.30   5.643%   $149.2736   $149.27   $149.25   $149.30  
  Purchase #3 $196.28   6.395%   $208.8321   $208.83   $208.85   $208.80  
  Purchase #4 $76.81   7.581%   $82.633   $82.63   $82.65   $82.60  
  Purchase #5 $147.36   9.739%   $161.7114   $161.71   $161.70   $161.70  
  Purchase #6 $141.56   6.444%   $150.6821   $150.68   $150.70   $150.70  
  Purchase #7 $195.49   5.616%   $206.4687   $206.47   $206.45   $206.50  
  7 purchase totals = $957.39       $1,021.5171   $1,021.51   $1,021.50   $1,021.50