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 $208.70   8.282%   $225.9845   $225.98   $226.00   $226.00  
  Purchase #2 $86.94   9.449%   $95.155   $95.16   $95.15   $95.20  
  Purchase #3 $160.72   3.223%   $165.9   $165.90   $165.90   $165.90  
  Purchase #4 $220.48   3.775%   $228.8031   $228.80   $228.80   $228.80  
  Purchase #5 $109.75   12.498%   $123.4666   $123.47   $123.45   $123.50  
  Purchase #6 $103.55   13.758%   $117.7964   $117.80   $117.80   $117.80  
  Purchase #7 $42.99   10.123%   $47.3419   $47.34   $47.35   $47.30  
  7 purchase totals = $933.13       $1,004.4475   $1,004.45   $1,004.45   $1,004.50