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 $225.89   10.489%   $249.5836   $249.58   $249.60   $249.60  
  Purchase #2 $187.63   13.285%   $212.5566   $212.56   $212.55   $212.60  
  Purchase #3 $230.78   11.697%   $257.7743   $257.77   $257.75   $257.80  
  Purchase #4 $23.79   7.720%   $25.6266   $25.63   $25.65   $25.60  
  Purchase #5 $73.71   12.641%   $83.0277   $83.03   $83.05   $83.00  
  Purchase #6 $17.74   3.627%   $18.3834   $18.38   $18.40   $18.40  
  Purchase #7 $196.34   12.768%   $221.4087   $221.41   $221.40   $221.40  
  7 purchase totals = $955.88       $1,068.3609   $1,068.36   $1,068.40   $1,068.40