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 $237.35   10.218%   $261.6024   $261.60   $261.60   $261.60  
  Purchase #2 $188.51   12.795%   $212.6299   $212.63   $212.65   $212.60  
  Purchase #3 $34.54   13.283%   $39.1279   $39.13   $39.15   $39.10  
  Purchase #4 $53.57   13.222%   $60.653   $60.65   $60.65   $60.70  
  Purchase #5 $187.43   10.659%   $207.4082   $207.41   $207.40   $207.40  
  Purchase #6 $101.28   12.123%   $113.5582   $113.56   $113.55   $113.60  
  Purchase #7 $195.38   9.152%   $213.2612   $213.26   $213.25   $213.30  
  7 purchase totals = $998.06       $1,108.2408   $1,108.24   $1,108.25   $1,108.30