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 $194.99   8.310%   $211.1937   $211.19   $211.20   $211.20  
  Purchase #2 $121.74   10.568%   $134.6055   $134.61   $134.60   $134.60  
  Purchase #3 $54.70   6.492%   $58.2511   $58.25   $58.25   $58.30  
  Purchase #4 $169.44   10.674%   $187.526   $187.53   $187.55   $187.50  
  Purchase #5 $204.96   4.397%   $213.9721   $213.97   $213.95   $214.00  
  Purchase #6 $19.64   6.263%   $20.8701   $20.87   $20.85   $20.90  
  Purchase #7 $125.54   9.361%   $137.2918   $137.29   $137.30   $137.30  
  7 purchase totals = $891.01       $963.7103   $963.71   $963.70   $963.80