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 $241.99   10.445%   $267.2659   $267.27   $267.25   $267.30  
  Purchase #2 $73.60   12.195%   $82.5755   $82.58   $82.60   $82.60  
  Purchase #3 $208.38   8.279%   $225.6318   $225.63   $225.65   $225.60  
  Purchase #4 $63.47   6.156%   $67.3772   $67.38   $67.40   $67.40  
  Purchase #5 $236.30   5.553%   $249.4217   $249.42   $249.40   $249.40  
  Purchase #6 $59.65   8.514%   $64.7286   $64.73   $64.75   $64.70  
  Purchase #7 $93.26   8.428%   $101.12   $101.12   $101.10   $101.10  
  7 purchase totals = $976.65       $1,058.1207   $1,058.13   $1,058.15   $1,058.10