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 $207.92   6.429%   $221.2872   $221.29   $221.30   $221.30  
  Purchase #2 $135.42   12.353%   $152.1484   $152.15   $152.15   $152.10  
  Purchase #3 $202.34   13.161%   $228.97   $228.97   $228.95   $229.00  
  Purchase #4 $158.43   13.294%   $179.4917   $179.49   $179.50   $179.50  
  Purchase #5 $148.82   8.648%   $161.69   $161.69   $161.70   $161.70  
  Purchase #6 $5.27   4.289%   $5.496   $5.50   $5.50   $5.50  
  Purchase #7 $217.77   8.347%   $235.9473   $235.95   $235.95   $235.90  
  7 purchase totals = $1,075.97       $1,185.0306   $1,185.04   $1,185.05   $1,185.00