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 $223.50   10.769%   $247.5687   $247.57   $247.55   $247.60  
  Purchase #2 $182.77   13.354%   $207.1771   $207.18   $207.20   $207.20  
  Purchase #3 $54.99   3.237%   $56.77   $56.77   $56.75   $56.80  
  Purchase #4 $199.56   10.567%   $220.6475   $220.65   $220.65   $220.60  
  Purchase #5 $126.63   4.135%   $131.8662   $131.87   $131.85   $131.90  
  Purchase #6 $49.48   4.505%   $51.7091   $51.71   $51.70   $51.70  
  Purchase #7 $148.35   11.545%   $165.477   $165.48   $165.50   $165.50  
  7 purchase totals = $985.28       $1,081.2156   $1,081.23   $1,081.20   $1,081.30