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 $87.42   8.503%   $94.8533   $94.85   $94.85   $94.90  
  Purchase #2 $188.69   13.500%   $214.1632   $214.16   $214.15   $214.20  
  Purchase #3 $146.26   3.243%   $151.0032   $151.00   $151.00   $151.00  
  Purchase #4 $170.94   5.646%   $180.5913   $180.59   $180.60   $180.60  
  Purchase #5 $114.55   12.874%   $129.2972   $129.30   $129.30   $129.30  
  Purchase #6 $199.99   5.582%   $211.1534   $211.15   $211.15   $211.20  
  Purchase #7 $71.30   3.261%   $73.6251   $73.63   $73.65   $73.60  
  7 purchase totals = $979.15       $1,054.6867   $1,054.68   $1,054.70   $1,054.80