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 $244.92   7.455%   $263.1788   $263.18   $263.20   $263.20  
  Purchase #2 $93.27   5.787%   $98.6675   $98.67   $98.65   $98.70  
  Purchase #3 $162.59   8.824%   $176.9369   $176.94   $176.95   $176.90  
  Purchase #4 $174.59   6.469%   $185.8842   $185.88   $185.90   $185.90  
  Purchase #5 $138.86   6.261%   $147.554   $147.55   $147.55   $147.60  
  Purchase #6 $188.83   12.131%   $211.737   $211.74   $211.75   $211.70  
  Purchase #7 $223.48   11.607%   $249.4193   $249.42   $249.40   $249.40  
  7 purchase totals = $1,226.54       $1,333.3777   $1,333.38   $1,333.40   $1,333.40