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 $51.63   10.405%   $57.0021   $57.00   $57.00   $57.00  
  Purchase #2 $235.48   13.407%   $267.0508   $267.05   $267.05   $267.10  
  Purchase #3 $80.81   4.792%   $84.6824   $84.68   $84.70   $84.70  
  Purchase #4 $119.54   8.140%   $129.2706   $129.27   $129.25   $129.30  
  Purchase #5 $142.80   9.501%   $156.3674   $156.37   $156.35   $156.40  
  Purchase #6 $196.97   8.548%   $213.807   $213.81   $213.80   $213.80  
  Purchase #7 $116.87   13.668%   $132.8438   $132.84   $132.85   $132.80  
  7 purchase totals = $944.10       $1,041.0241   $1,041.02   $1,041.00   $1,041.10