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 $89.85   13.824%   $102.2709   $102.27   $102.25   $102.30  
  Purchase #2 $63.41   5.396%   $66.8316   $66.83   $66.85   $66.80  
  Purchase #3 $67.48   12.557%   $75.9535   $75.95   $75.95   $76.00  
  Purchase #4 $225.79   5.748%   $238.7684   $238.77   $238.75   $238.80  
  Purchase #5 $248.95   11.699%   $278.0747   $278.07   $278.05   $278.10  
  Purchase #6 $129.56   7.564%   $139.3599   $139.36   $139.35   $139.40  
  Purchase #7 $120.80   3.602%   $125.1512   $125.15   $125.15   $125.20  
  7 purchase totals = $945.84       $1,026.4102   $1,026.40   $1,026.35   $1,026.60