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 $161.78   13.733%   $183.9972   $184.00   $184.00   $184.00  
  Purchase #2 $213.57   13.620%   $242.6582   $242.66   $242.65   $242.70  
  Purchase #3 $175.45   7.351%   $188.3473   $188.35   $188.35   $188.30  
  Purchase #4 $173.84   6.115%   $184.4703   $184.47   $184.45   $184.50  
  Purchase #5 $192.49   4.312%   $200.7902   $200.79   $200.80   $200.80  
  Purchase #6 $236.43   7.711%   $254.6611   $254.66   $254.65   $254.70  
  Purchase #7 $206.36   13.727%   $234.687   $234.69   $234.70   $234.70  
  7 purchase totals = $1,359.92       $1,489.6113   $1,489.62   $1,489.60   $1,489.70