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 $76.76   5.648%   $81.0954   $81.10   $81.10   $81.10  
  Purchase #2 $98.72   13.803%   $112.3463   $112.35   $112.35   $112.30  
  Purchase #3 $71.50   7.330%   $76.741   $76.74   $76.75   $76.70  
  Purchase #4 $250.59   7.417%   $269.1763   $269.18   $269.20   $269.20  
  Purchase #5 $210.62   9.340%   $230.2919   $230.29   $230.30   $230.30  
  Purchase #6 $166.80   5.417%   $175.8356   $175.84   $175.85   $175.80  
  Purchase #7 $94.74   13.692%   $107.7118   $107.71   $107.70   $107.70  
  7 purchase totals = $969.73       $1,053.1983   $1,053.21   $1,053.25   $1,053.10