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 $27.62   3.536%   $28.5966   $28.60   $28.60   $28.60  
  Purchase #2 $107.85   12.498%   $121.3291   $121.33   $121.35   $121.30  
  Purchase #3 $195.58   10.115%   $215.3629   $215.36   $215.35   $215.40  
  Purchase #4 $240.95   3.819%   $250.1519   $250.15   $250.15   $250.20  
  Purchase #5 $145.47   10.528%   $160.7851   $160.79   $160.80   $160.80  
  Purchase #6 $238.59   4.569%   $249.4912   $249.49   $249.50   $249.50  
  Purchase #7 $196.37   4.721%   $205.6406   $205.64   $205.65   $205.60  
  7 purchase totals = $1,152.43       $1,231.3574   $1,231.36   $1,231.40   $1,231.40