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 $241.64   5.526%   $254.993   $254.99   $255.00   $255.00  
  Purchase #2 $171.49   9.874%   $188.4229   $188.42   $188.40   $188.40  
  Purchase #3 $36.38   13.529%   $41.3019   $41.30   $41.30   $41.30  
  Purchase #4 $50.88   13.516%   $57.7569   $57.76   $57.75   $57.80  
  Purchase #5 $194.35   12.124%   $217.913   $217.91   $217.90   $217.90  
  Purchase #6 $88.27   5.320%   $92.966   $92.97   $92.95   $93.00  
  Purchase #7 $152.76   12.377%   $171.6671   $171.67   $171.65   $171.70  
  7 purchase totals = $935.77       $1,025.0208   $1,025.02   $1,024.95   $1,025.10