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 $218.44   8.249%   $236.4591   $236.46   $236.45   $236.50  
  Purchase #2 $227.83   10.691%   $252.1873   $252.19   $252.20   $252.20  
  Purchase #3 $56.43   6.389%   $60.0353   $60.04   $60.05   $60.00  
  Purchase #4 $138.95   7.121%   $148.8446   $148.84   $148.85   $148.80  
  Purchase #5 $76.57   9.170%   $83.5915   $83.59   $83.60   $83.60  
  Purchase #6 $221.96   11.571%   $247.643   $247.64   $247.65   $247.60  
  Purchase #7 $49.49   4.710%   $51.821   $51.82   $51.80   $51.80  
  7 purchase totals = $989.67       $1,080.5818   $1,080.58   $1,080.60   $1,080.50