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 $237.39   11.728%   $265.2311   $265.23   $265.25   $265.20  
  Purchase #2 $36.46   10.340%   $40.23   $40.23   $40.25   $40.20  
  Purchase #3 $242.92   6.637%   $259.0426   $259.04   $259.05   $259.00  
  Purchase #4 $196.99   7.400%   $211.5673   $211.57   $211.55   $211.60  
  Purchase #5 $152.30   10.574%   $168.4042   $168.40   $168.40   $168.40  
  Purchase #6 $26.43   5.726%   $27.9434   $27.94   $27.95   $27.90  
  Purchase #7 $138.82   9.503%   $152.0121   $152.01   $152.00   $152.00  
  7 purchase totals = $1,031.31       $1,124.4307   $1,124.42   $1,124.45   $1,124.30