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 $62.40   13.277%   $70.6848   $70.68   $70.70   $70.70  
  Purchase #2 $51.98   8.811%   $56.56   $56.56   $56.55   $56.60  
  Purchase #3 $126.70   8.560%   $137.5455   $137.55   $137.55   $137.50  
  Purchase #4 $203.96   4.853%   $213.8582   $213.86   $213.85   $213.90  
  Purchase #5 $67.25   8.371%   $72.8795   $72.88   $72.90   $72.90  
  Purchase #6 $140.53   11.857%   $157.1926   $157.19   $157.20   $157.20  
  Purchase #7 $113.57   4.496%   $118.6761   $118.68   $118.70   $118.70  
  7 purchase totals = $766.39       $827.3967   $827.40   $827.45   $827.50