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 $198.79   13.194%   $225.0184   $225.02   $225.00   $225.00  
  Purchase #2 $228.65   8.162%   $247.3124   $247.31   $247.30   $247.30  
  Purchase #3 $209.58   10.854%   $232.3278   $232.33   $232.35   $232.30  
  Purchase #4 $25.57   3.635%   $26.4995   $26.50   $26.50   $26.50  
  Purchase #5 $62.93   12.650%   $70.8906   $70.89   $70.90   $70.90  
  Purchase #6 $92.49   3.584%   $95.8048   $95.80   $95.80   $95.80  
  Purchase #7 $236.36   13.412%   $268.0606   $268.06   $268.05   $268.10  
  7 purchase totals = $1,054.37       $1,165.9141   $1,165.91   $1,165.90   $1,165.90