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 $247.27   6.308%   $262.8678   $262.87   $262.85   $262.90  
  Purchase #2 $217.88   5.535%   $229.9397   $229.94   $229.95   $229.90  
  Purchase #3 $30.87   6.676%   $32.9309   $32.93   $32.95   $32.90  
  Purchase #4 $101.43   7.621%   $109.16   $109.16   $109.15   $109.20  
  Purchase #5 $191.41   4.321%   $199.6808   $199.68   $199.70   $199.70  
  Purchase #6 $175.35   10.698%   $194.1089   $194.11   $194.10   $194.10  
  Purchase #7 $24.85   5.488%   $26.2138   $26.21   $26.20   $26.20  
  7 purchase totals = $989.06       $1,054.9019   $1,054.90   $1,054.90   $1,054.90