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 $60.34   11.583%   $67.3292   $67.33   $67.35   $67.30  
  Purchase #2 $77.27   13.181%   $87.455   $87.46   $87.45   $87.50  
  Purchase #3 $230.42   4.694%   $241.2359   $241.24   $241.25   $241.20  
  Purchase #4 $81.28   12.701%   $91.6034   $91.60   $91.60   $91.60  
  Purchase #5 $18.63   10.642%   $20.6126   $20.61   $20.60   $20.60  
  Purchase #6 $179.47   3.700%   $186.1104   $186.11   $186.10   $186.10  
  Purchase #7 $56.68   6.230%   $60.2112   $60.21   $60.20   $60.20  
  7 purchase totals = $704.09       $754.5577   $754.56   $754.55   $754.50