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 $241.59   3.337%   $249.6519   $249.65   $249.65   $249.70  
  Purchase #2 $18.41   13.616%   $20.9167   $20.92   $20.90   $20.90  
  Purchase #3 $24.63   3.394%   $25.4659   $25.47   $25.45   $25.50  
  Purchase #4 $194.95   6.130%   $206.9004   $206.90   $206.90   $206.90  
  Purchase #5 $105.65   7.734%   $113.821   $113.82   $113.80   $113.80  
  Purchase #6 $25.53   12.131%   $28.627   $28.63   $28.65   $28.60  
  Purchase #7 $132.30   6.215%   $140.5224   $140.52   $140.50   $140.50  
  7 purchase totals = $743.06       $785.9053   $785.91   $785.85   $785.90