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 $54.38   13.202%   $61.5592   $61.56   $61.55   $61.60  
  Purchase #2 $178.51   7.215%   $191.3895   $191.39   $191.40   $191.40  
  Purchase #3 $84.88   7.370%   $91.1357   $91.14   $91.15   $91.10  
  Purchase #4 $243.33   8.665%   $264.4145   $264.41   $264.40   $264.40  
  Purchase #5 $92.92   13.801%   $105.7439   $105.74   $105.75   $105.70  
  Purchase #6 $134.56   5.690%   $142.2165   $142.22   $142.20   $142.20  
  Purchase #7 $144.41   3.683%   $149.7286   $149.73   $149.75   $149.70  
  7 purchase totals = $932.99       $1,006.1879   $1,006.19   $1,006.20   $1,006.10