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 $163.53   8.162%   $176.8773   $176.88   $176.90   $176.90  
  Purchase #2 $118.34   5.241%   $124.5422   $124.54   $124.55   $124.50  
  Purchase #3 $18.38   11.777%   $20.5446   $20.54   $20.55   $20.50  
  Purchase #4 $234.63   6.345%   $249.5173   $249.52   $249.50   $249.50  
  Purchase #5 $112.93   12.435%   $126.9728   $126.97   $126.95   $127.00  
  Purchase #6 $154.57   7.575%   $166.2787   $166.28   $166.30   $166.30  
  Purchase #7 $144.90   11.596%   $161.7026   $161.70   $161.70   $161.70  
  7 purchase totals = $947.28       $1,026.4355   $1,026.43   $1,026.45   $1,026.40