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 $62.92   12.317%   $70.6699   $70.67   $70.65   $70.70  
  Purchase #2 $92.31   12.767%   $104.0952   $104.10   $104.10   $104.10  
  Purchase #3 $166.62   9.586%   $182.5922   $182.59   $182.60   $182.60  
  Purchase #4 $72.84   7.184%   $78.0728   $78.07   $78.05   $78.10  
  Purchase #5 $24.75   5.306%   $26.0632   $26.06   $26.05   $26.10  
  Purchase #6 $50.56   5.294%   $53.2366   $53.24   $53.25   $53.20  
  Purchase #7 $216.58   11.205%   $240.8478   $240.85   $240.85   $240.80  
  7 purchase totals = $686.58       $755.5777   $755.58   $755.55   $755.60