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 $214.67   11.222%   $238.7603   $238.76   $238.75   $238.80  
  Purchase #2 $179.34   5.143%   $188.5635   $188.56   $188.55   $188.60  
  Purchase #3 $127.51   3.461%   $131.9231   $131.92   $131.90   $131.90  
  Purchase #4 $218.66   11.544%   $243.9021   $243.90   $243.90   $243.90  
  Purchase #5 $179.36   8.567%   $194.7258   $194.73   $194.75   $194.70  
  Purchase #6 $217.50   5.275%   $228.9731   $228.97   $228.95   $229.00  
  Purchase #7 $116.71   10.736%   $129.24   $129.24   $129.25   $129.20  
  7 purchase totals = $1,253.75       $1,356.0879   $1,356.08   $1,356.05   $1,356.10