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 $206.25   3.263%   $212.9799   $212.98   $213.00   $213.00  
  Purchase #2 $187.29   5.688%   $197.9431   $197.94   $197.95   $197.90  
  Purchase #3 $29.46   9.563%   $32.2773   $32.28   $32.30   $32.30  
  Purchase #4 $36.64   8.170%   $39.6335   $39.63   $39.65   $39.60  
  Purchase #5 $230.78   8.315%   $249.9694   $249.97   $249.95   $250.00  
  Purchase #6 $200.86   7.637%   $216.1997   $216.20   $216.20   $216.20  
  Purchase #7 $150.69   12.729%   $169.8713   $169.87   $169.85   $169.90  
  7 purchase totals = $1,041.97       $1,118.8742   $1,118.87   $1,118.90   $1,118.90