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 $59.58   13.364%   $67.5423   $67.54   $67.55   $67.50  
  Purchase #2 $225.64   10.641%   $249.6504   $249.65   $249.65   $249.70  
  Purchase #3 $46.48   12.287%   $52.191   $52.19   $52.20   $52.20  
  Purchase #4 $113.69   3.196%   $117.3235   $117.32   $117.30   $117.30  
  Purchase #5 $230.64   6.507%   $245.6477   $245.65   $245.65   $245.60  
  Purchase #6 $27.99   6.185%   $29.7212   $29.72   $29.70   $29.70  
  Purchase #7 $57.76   8.735%   $62.8053   $62.81   $62.80   $62.80  
  7 purchase totals = $761.78       $824.8814   $824.88   $824.85   $824.80