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 $62.32   11.835%   $69.6956   $69.70   $69.70   $69.70  
  Purchase #2 $182.38   11.382%   $203.1385   $203.14   $203.15   $203.10  
  Purchase #3 $129.44   7.469%   $139.1079   $139.11   $139.10   $139.10  
  Purchase #4 $206.95   7.205%   $221.8607   $221.86   $221.85   $221.90  
  Purchase #5 $6.48   7.124%   $6.9416   $6.94   $6.95   $6.90  
  Purchase #6 $133.30   11.658%   $148.8401   $148.84   $148.85   $148.80  
  Purchase #7 $209.51   13.420%   $237.6262   $237.63   $237.65   $237.60  
  7 purchase totals = $930.38       $1,027.2106   $1,027.22   $1,027.25   $1,027.10