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 $196.95   5.464%   $207.7113   $207.71   $207.70   $207.70  
  Purchase #2 $56.64   8.800%   $61.6243   $61.62   $61.60   $61.60  
  Purchase #3 $81.49   11.131%   $90.5607   $90.56   $90.55   $90.60  
  Purchase #4 $79.70   6.234%   $84.6685   $84.67   $84.65   $84.70  
  Purchase #5 $240.68   7.118%   $257.8116   $257.81   $257.80   $257.80  
  Purchase #6 $69.79   10.365%   $77.0237   $77.02   $77.00   $77.00  
  Purchase #7 $88.55   4.105%   $92.185   $92.19   $92.20   $92.20  
  7 purchase totals = $813.80       $871.5851   $871.58   $871.50   $871.60