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 $88.36   8.630%   $95.9855   $95.99   $96.00   $96.00  
  Purchase #2 $169.87   6.664%   $181.1901   $181.19   $181.20   $181.20  
  Purchase #3 $184.44   7.801%   $198.8282   $198.83   $198.85   $198.80  
  Purchase #4 $147.92   11.216%   $164.5107   $164.51   $164.50   $164.50  
  Purchase #5 $30.64   12.404%   $34.4406   $34.44   $34.45   $34.40  
  Purchase #6 $63.73   13.583%   $72.3864   $72.39   $72.40   $72.40  
  Purchase #7 $203.35   10.442%   $224.5838   $224.58   $224.60   $224.60  
  7 purchase totals = $888.31       $971.9253   $971.93   $972.00   $971.90