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 $84.46   8.149%   $91.3426   $91.34   $91.35   $91.30  
  Purchase #2 $176.49   6.747%   $188.3978   $188.40   $188.40   $188.40  
  Purchase #3 $162.26   8.677%   $176.3393   $176.34   $176.35   $176.30  
  Purchase #4 $60.89   10.320%   $67.1738   $67.17   $67.15   $67.20  
  Purchase #5 $119.93   5.667%   $126.7264   $126.73   $126.75   $126.70  
  Purchase #6 $6.97   5.253%   $7.3361   $7.34   $7.35   $7.30  
  Purchase #7 $95.94   8.385%   $103.9846   $103.98   $104.00   $104.00  
  7 purchase totals = $706.94       $761.3006   $761.30   $761.35   $761.20