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 $245.90   3.373%   $254.1942   $254.19   $254.20   $254.20  
  Purchase #2 $40.59   13.820%   $46.1995   $46.20   $46.20   $46.20  
  Purchase #3 $171.25   12.623%   $192.8669   $192.87   $192.85   $192.90  
  Purchase #4 $157.36   13.761%   $179.0143   $179.01   $179.00   $179.00  
  Purchase #5 $88.42   8.715%   $96.1258   $96.13   $96.15   $96.10  
  Purchase #6 $11.40   12.154%   $12.7856   $12.79   $12.80   $12.80  
  Purchase #7 $24.49   7.774%   $26.3939   $26.39   $26.40   $26.40  
  7 purchase totals = $739.41       $807.5802   $807.58   $807.60   $807.60