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 $214.39   11.432%   $238.8991   $238.90   $238.90   $238.90  
  Purchase #2 $165.97   4.365%   $173.2146   $173.21   $173.20   $173.20  
  Purchase #3 $170.85   8.188%   $184.8392   $184.84   $184.85   $184.80  
  Purchase #4 $22.68   5.161%   $23.8505   $23.85   $23.85   $23.90  
  Purchase #5 $182.86   6.468%   $194.6874   $194.69   $194.70   $194.70  
  Purchase #6 $249.94   6.865%   $267.0984   $267.10   $267.10   $267.10  
  Purchase #7 $228.96   10.373%   $252.71   $252.71   $252.70   $252.70  
  7 purchase totals = $1,235.65       $1,335.2992   $1,335.30   $1,335.30   $1,335.30