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 $77.97   5.603%   $82.3387   $82.34   $82.35   $82.30  
  Purchase #2 $113.37   6.140%   $120.3309   $120.33   $120.35   $120.30  
  Purchase #3 $96.62   10.775%   $107.0308   $107.03   $107.05   $107.00  
  Purchase #4 $226.91   9.149%   $247.67   $247.67   $247.65   $247.70  
  Purchase #5 $126.85   5.423%   $133.7291   $133.73   $133.75   $133.70  
  Purchase #6 $134.67   5.733%   $142.3906   $142.39   $142.40   $142.40  
  Purchase #7 $230.61   13.185%   $261.0159   $261.02   $261.00   $261.00  
  7 purchase totals = $1,007.00       $1,094.5060   $1,094.51   $1,094.55   $1,094.40