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 $209.98   11.791%   $234.7387   $234.74   $234.75   $234.70  
  Purchase #2 $174.85   10.240%   $192.7546   $192.75   $192.75   $192.80  
  Purchase #3 $218.56   12.870%   $246.6887   $246.69   $246.70   $246.70  
  Purchase #4 $57.96   4.689%   $60.6777   $60.68   $60.70   $60.70  
  Purchase #5 $112.38   9.258%   $122.7841   $122.78   $122.80   $122.80  
  Purchase #6 $34.56   11.646%   $38.5849   $38.58   $38.60   $38.60  
  Purchase #7 $140.67   5.550%   $148.4772   $148.48   $148.50   $148.50  
  7 purchase totals = $948.96       $1,044.7059   $1,044.70   $1,044.80   $1,044.80