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 $216.55   11.571%   $241.607   $241.61   $241.60   $241.60  
  Purchase #2 $157.30   11.341%   $175.1394   $175.14   $175.15   $175.10  
  Purchase #3 $102.27   10.303%   $112.8069   $112.81   $112.80   $112.80  
  Purchase #4 $132.31   6.824%   $141.3388   $141.34   $141.35   $141.30  
  Purchase #5 $140.97   13.424%   $159.8938   $159.89   $159.90   $159.90  
  Purchase #6 $135.47   8.150%   $146.5108   $146.51   $146.50   $146.50  
  Purchase #7 $117.43   10.165%   $129.3668   $129.37   $129.35   $129.40  
  7 purchase totals = $1,002.30       $1,106.6635   $1,106.67   $1,106.65   $1,106.60