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 $22.64   6.218%   $24.0478   $24.05   $24.05   $24.00  
  Purchase #2 $170.57   5.798%   $180.4596   $180.46   $180.45   $180.50  
  Purchase #3 $91.27   13.370%   $103.4728   $103.47   $103.45   $103.50  
  Purchase #4 $179.97   4.321%   $187.7465   $187.75   $187.75   $187.70  
  Purchase #5 $152.73   7.225%   $163.7647   $163.76   $163.75   $163.80  
  Purchase #6 $159.81   9.527%   $175.0351   $175.04   $175.05   $175.00  
  Purchase #7 $204.95   5.305%   $215.8226   $215.82   $215.80   $215.80  
  7 purchase totals = $981.94       $1,050.3491   $1,050.35   $1,050.30   $1,050.30