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 $210.43   13.467%   $238.7686   $238.77   $238.75   $238.80  
  Purchase #2 $243.30   3.534%   $251.8982   $251.90   $251.90   $251.90  
  Purchase #3 $165.92   5.768%   $175.4903   $175.49   $175.50   $175.50  
  Purchase #4 $23.63   10.751%   $26.1705   $26.17   $26.15   $26.20  
  Purchase #5 $229.94   5.508%   $242.6051   $242.61   $242.60   $242.60  
  Purchase #6 $43.90   13.778%   $49.9485   $49.95   $49.95   $49.90  
  Purchase #7 $173.80   7.217%   $186.3431   $186.34   $186.35   $186.30  
  7 purchase totals = $1,090.92       $1,171.2243   $1,171.23   $1,171.20   $1,171.20