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 $85.87   13.739%   $97.6677   $97.67   $97.65   $97.70  
  Purchase #2 $126.48   11.342%   $140.8254   $140.83   $140.85   $140.80  
  Purchase #3 $156.71   5.443%   $165.2397   $165.24   $165.25   $165.20  
  Purchase #4 $246.94   3.673%   $256.0101   $256.01   $256.00   $256.00  
  Purchase #5 $71.71   9.475%   $78.5045   $78.50   $78.50   $78.50  
  Purchase #6 $96.44   4.772%   $101.0421   $101.04   $101.05   $101.00  
  Purchase #7 $147.55   9.730%   $161.9066   $161.91   $161.90   $161.90  
  7 purchase totals = $931.70       $1,001.1961   $1,001.20   $1,001.20   $1,001.10