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 $84.73   9.561%   $92.831   $92.83   $92.85   $92.80  
  Purchase #2 $57.28   7.728%   $61.7066   $61.71   $61.70   $61.70  
  Purchase #3 $210.43   10.537%   $232.603   $232.60   $232.60   $232.60  
  Purchase #4 $194.63   9.807%   $213.7174   $213.72   $213.70   $213.70  
  Purchase #5 $135.71   4.816%   $142.2458   $142.25   $142.25   $142.20  
  Purchase #6 $158.55   7.630%   $170.6474   $170.65   $170.65   $170.60  
  Purchase #7 $78.65   6.268%   $83.5798   $83.58   $83.60   $83.60  
  7 purchase totals = $919.98       $997.3310   $997.34   $997.35   $997.20