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 $63.60   11.861%   $71.1436   $71.14   $71.15   $71.10  
  Purchase #2 $75.55   10.605%   $83.5621   $83.56   $83.55   $83.60  
  Purchase #3 $118.80   8.415%   $128.797   $128.80   $128.80   $128.80  
  Purchase #4 $186.48   3.542%   $193.0851   $193.09   $193.10   $193.10  
  Purchase #5 $229.69   7.711%   $247.4014   $247.40   $247.40   $247.40  
  Purchase #6 $23.95   7.833%   $25.826   $25.83   $25.85   $25.80  
  Purchase #7 $136.27   7.304%   $146.2232   $146.22   $146.20   $146.20  
  7 purchase totals = $834.34       $896.0384   $896.04   $896.05   $896.00