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 $245.65   8.841%   $267.3679   $267.37   $267.35   $267.40  
  Purchase #2 $241.45   12.593%   $271.8558   $271.86   $271.85   $271.90  
  Purchase #3 $120.56   3.775%   $125.1111   $125.11   $125.10   $125.10  
  Purchase #4 $232.45   7.235%   $249.2678   $249.27   $249.25   $249.30  
  Purchase #5 $235.67   5.460%   $248.5376   $248.54   $248.55   $248.50  
  Purchase #6 $103.48   13.716%   $117.6733   $117.67   $117.65   $117.70  
  Purchase #7 $152.49   6.822%   $162.8929   $162.89   $162.90   $162.90  
  7 purchase totals = $1,331.75       $1,442.7064   $1,442.71   $1,442.65   $1,442.80