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 $233.50   12.283%   $262.1808   $262.18   $262.20   $262.20  
  Purchase #2 $167.87   9.557%   $183.9133   $183.91   $183.90   $183.90  
  Purchase #3 $64.86   8.167%   $70.1571   $70.16   $70.15   $70.20  
  Purchase #4 $168.87   12.126%   $189.3472   $189.35   $189.35   $189.30  
  Purchase #5 $29.94   10.735%   $33.1541   $33.15   $33.15   $33.20  
  Purchase #6 $106.45   12.679%   $119.9468   $119.95   $119.95   $119.90  
  Purchase #7 $195.49   6.116%   $207.4462   $207.45   $207.45   $207.40  
  7 purchase totals = $966.98       $1,066.1455   $1,066.15   $1,066.15   $1,066.10