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 $58.94   10.113%   $64.9006   $64.90   $64.90   $64.90  
  Purchase #2 $235.51   11.643%   $262.9304   $262.93   $262.95   $262.90  
  Purchase #3 $135.41   6.507%   $144.2211   $144.22   $144.20   $144.20  
  Purchase #4 $117.53   4.295%   $122.5779   $122.58   $122.60   $122.60  
  Purchase #5 $167.48   13.694%   $190.4147   $190.41   $190.40   $190.40  
  Purchase #6 $136.45   10.717%   $151.0733   $151.07   $151.05   $151.10  
  Purchase #7 $92.51   6.561%   $98.5796   $98.58   $98.60   $98.60  
  7 purchase totals = $943.83       $1,034.6976   $1,034.69   $1,034.70   $1,034.70