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 $225.69   3.654%   $233.9367   $233.94   $233.95   $233.90  
  Purchase #2 $177.25   9.824%   $194.663   $194.66   $194.65   $194.70  
  Purchase #3 $63.87   9.430%   $69.8929   $69.89   $69.90   $69.90  
  Purchase #4 $250.28   9.295%   $273.5435   $273.54   $273.55   $273.50  
  Purchase #5 $245.71   13.547%   $278.9963   $279.00   $279.00   $279.00  
  Purchase #6 $121.54   13.262%   $137.6586   $137.66   $137.65   $137.70  
  Purchase #7 $234.53   5.566%   $247.5839   $247.58   $247.60   $247.60  
  7 purchase totals = $1,318.87       $1,436.2749   $1,436.27   $1,436.30   $1,436.30