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 $161.49   8.745%   $175.6123   $175.61   $175.60   $175.60  
  Purchase #2 $137.91   12.137%   $154.6481   $154.65   $154.65   $154.60  
  Purchase #3 $53.83   11.686%   $60.1206   $60.12   $60.10   $60.10  
  Purchase #4 $10.79   8.518%   $11.7091   $11.71   $11.70   $11.70  
  Purchase #5 $139.87   10.186%   $154.1172   $154.12   $154.10   $154.10  
  Purchase #6 $215.53   12.553%   $242.5855   $242.59   $242.60   $242.60  
  Purchase #7 $161.78   13.182%   $183.1058   $183.11   $183.10   $183.10  
  7 purchase totals = $881.20       $981.8986   $981.91   $981.85   $981.80