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 $174.26   12.299%   $195.6922   $195.69   $195.70   $195.70  
  Purchase #2 $57.35   13.640%   $65.1725   $65.17   $65.15   $65.20  
  Purchase #3 $218.46   4.320%   $227.8975   $227.90   $227.90   $227.90  
  Purchase #4 $55.36   4.119%   $57.6403   $57.64   $57.65   $57.60  
  Purchase #5 $92.66   5.471%   $97.7294   $97.73   $97.75   $97.70  
  Purchase #6 $195.96   8.219%   $212.066   $212.07   $212.05   $212.10  
  Purchase #7 $138.77   7.505%   $149.1847   $149.18   $149.20   $149.20  
  7 purchase totals = $932.82       $1,005.3826   $1,005.38   $1,005.40   $1,005.40