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 $235.63   13.537%   $267.5272   $267.53   $267.55   $267.50  
  Purchase #2 $83.78   10.718%   $92.7595   $92.76   $92.75   $92.80  
  Purchase #3 $117.99   4.840%   $123.7007   $123.70   $123.70   $123.70  
  Purchase #4 $94.99   11.648%   $106.0544   $106.05   $106.05   $106.10  
  Purchase #5 $101.43   7.370%   $108.9054   $108.91   $108.90   $108.90  
  Purchase #6 $58.57   4.577%   $61.2507   $61.25   $61.25   $61.30  
  Purchase #7 $236.85   10.869%   $262.5932   $262.59   $262.60   $262.60  
  7 purchase totals = $929.24       $1,022.7911   $1,022.79   $1,022.80   $1,022.90