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 $105.41   9.611%   $115.541   $115.54   $115.55   $115.50  
  Purchase #2 $230.83   7.256%   $247.579   $247.58   $247.60   $247.60  
  Purchase #3 $118.59   11.130%   $131.7891   $131.79   $131.80   $131.80  
  Purchase #4 $70.27   5.209%   $73.9304   $73.93   $73.95   $73.90  
  Purchase #5 $207.98   9.620%   $227.9877   $227.99   $228.00   $228.00  
  Purchase #6 $63.38   7.741%   $68.2862   $68.29   $68.30   $68.30  
  Purchase #7 $22.37   9.847%   $24.5728   $24.57   $24.55   $24.60  
  7 purchase totals = $818.83       $889.6862   $889.69   $889.75   $889.70