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 $24.86   6.790%   $26.548   $26.55   $26.55   $26.50  
  Purchase #2 $59.83   3.691%   $62.0383   $62.04   $62.05   $62.00  
  Purchase #3 $61.47   10.458%   $67.8985   $67.90   $67.90   $67.90  
  Purchase #4 $49.28   10.211%   $54.312   $54.31   $54.30   $54.30  
  Purchase #5 $237.81   5.394%   $250.6375   $250.64   $250.65   $250.60  
  Purchase #6 $199.96   6.128%   $212.2135   $212.21   $212.20   $212.20  
  Purchase #7 $124.89   8.638%   $135.678   $135.68   $135.70   $135.70  
  7 purchase totals = $758.10       $809.3258   $809.33   $809.35   $809.20