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 $62.77   6.844%   $67.066   $67.07   $67.05   $67.10  
  Purchase #2 $45.96   9.506%   $50.329   $50.33   $50.35   $50.30  
  Purchase #3 $194.62   5.527%   $205.3766   $205.38   $205.40   $205.40  
  Purchase #4 $86.97   9.437%   $95.1774   $95.18   $95.20   $95.20  
  Purchase #5 $37.25   6.651%   $39.7275   $39.73   $39.75   $39.70  
  Purchase #6 $220.35   11.606%   $245.9238   $245.92   $245.90   $245.90  
  Purchase #7 $7.74   6.422%   $8.2371   $8.24   $8.25   $8.20  
  7 purchase totals = $655.66       $711.8374   $711.85   $711.90   $711.80