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 $169.66   11.451%   $189.0878   $189.09   $189.10   $189.10  
  Purchase #2 $243.82   7.495%   $262.0943   $262.09   $262.10   $262.10  
  Purchase #3 $47.59   4.135%   $49.5578   $49.56   $49.55   $49.60  
  Purchase #4 $182.82   13.173%   $206.9029   $206.90   $206.90   $206.90  
  Purchase #5 $142.68   13.347%   $161.7235   $161.72   $161.70   $161.70  
  Purchase #6 $17.40   5.343%   $18.3297   $18.33   $18.35   $18.30  
  Purchase #7 $122.79   11.312%   $136.68   $136.68   $136.70   $136.70  
  7 purchase totals = $926.76       $1,024.3760   $1,024.37   $1,024.40   $1,024.40