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 $238.30   13.106%   $269.5316   $269.53   $269.55   $269.50  
  Purchase #2 $165.56   6.238%   $175.8876   $175.89   $175.90   $175.90  
  Purchase #3 $30.95   6.415%   $32.9354   $32.94   $32.95   $32.90  
  Purchase #4 $159.36   3.535%   $164.9934   $164.99   $165.00   $165.00  
  Purchase #5 $12.64   12.283%   $14.1926   $14.19   $14.20   $14.20  
  Purchase #6 $26.73   5.770%   $28.2723   $28.27   $28.25   $28.30  
  Purchase #7 $149.50   8.173%   $161.7186   $161.72   $161.70   $161.70  
  7 purchase totals = $783.04       $847.5315   $847.53   $847.55   $847.50