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 $109.45   6.127%   $116.156   $116.16   $116.15   $116.20  
  Purchase #2 $211.86   3.301%   $218.8535   $218.85   $218.85   $218.90  
  Purchase #3 $58.37   10.781%   $64.6629   $64.66   $64.65   $64.70  
  Purchase #4 $37.29   10.572%   $41.2323   $41.23   $41.25   $41.20  
  Purchase #5 $88.69   7.323%   $95.1848   $95.18   $95.20   $95.20  
  Purchase #6 $186.75   11.603%   $208.4186   $208.42   $208.40   $208.40  
  Purchase #7 $161.32   12.765%   $181.9125   $181.91   $181.90   $181.90  
  7 purchase totals = $853.73       $926.4206   $926.41   $926.40   $926.50