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 $54.89   10.365%   $60.5793   $60.58   $60.60   $60.60  
  Purchase #2 $181.68   4.473%   $189.8065   $189.81   $189.80   $189.80  
  Purchase #3 $111.72   12.532%   $125.7208   $125.72   $125.70   $125.70  
  Purchase #4 $153.73   7.224%   $164.8355   $164.84   $164.85   $164.80  
  Purchase #5 $64.59   8.408%   $70.0207   $70.02   $70.00   $70.00  
  Purchase #6 $183.28   4.412%   $191.3663   $191.37   $191.35   $191.40  
  Purchase #7 $116.72   11.176%   $129.7646   $129.76   $129.75   $129.80  
  7 purchase totals = $866.61       $932.0937   $932.10   $932.05   $932.10