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 $246.74   8.203%   $266.9801   $266.98   $267.00   $267.00  
  Purchase #2 $101.73   12.523%   $114.4696   $114.47   $114.45   $114.50  
  Purchase #3 $243.41   8.834%   $264.9128   $264.91   $264.90   $264.90  
  Purchase #4 $16.77   10.610%   $18.5493   $18.55   $18.55   $18.50  
  Purchase #5 $146.44   5.208%   $154.0666   $154.07   $154.05   $154.10  
  Purchase #6 $187.64   9.184%   $204.8729   $204.87   $204.85   $204.90  
  Purchase #7 $212.96   5.560%   $224.8006   $224.80   $224.80   $224.80  
  7 purchase totals = $1,155.69       $1,248.6519   $1,248.65   $1,248.60   $1,248.70