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 $130.45   3.260%   $134.7027   $134.70   $134.70   $134.70  
  Purchase #2 $210.82   7.273%   $226.1529   $226.15   $226.15   $226.20  
  Purchase #3 $30.49   8.858%   $33.1908   $33.19   $33.20   $33.20  
  Purchase #4 $197.48   8.512%   $214.2895   $214.29   $214.30   $214.30  
  Purchase #5 $205.78   13.803%   $234.1838   $234.18   $234.20   $234.20  
  Purchase #6 $236.39   13.479%   $268.253   $268.25   $268.25   $268.30  
  Purchase #7 $74.73   13.301%   $84.6698   $84.67   $84.65   $84.70  
  7 purchase totals = $1,086.14       $1,195.4425   $1,195.43   $1,195.45   $1,195.60