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 $185.41   11.654%   $207.0177   $207.02   $207.00   $207.00  
  Purchase #2 $156.46   7.149%   $167.6453   $167.65   $167.65   $167.60  
  Purchase #3 $198.98   10.518%   $219.9087   $219.91   $219.90   $219.90  
  Purchase #4 $52.27   7.105%   $55.9838   $55.98   $56.00   $56.00  
  Purchase #5 $124.36   3.596%   $128.832   $128.83   $128.85   $128.80  
  Purchase #6 $8.37   7.409%   $8.9901   $8.99   $9.00   $9.00  
  Purchase #7 $105.39   10.424%   $116.3759   $116.38   $116.40   $116.40  
  7 purchase totals = $831.24       $904.7535   $904.76   $904.80   $904.70