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 $80.26   5.418%   $84.6085   $84.61   $84.60   $84.60  
  Purchase #2 $216.26   11.842%   $241.8695   $241.87   $241.85   $241.90  
  Purchase #3 $27.27   13.706%   $31.0076   $31.01   $31.00   $31.00  
  Purchase #4 $102.73   6.841%   $109.7578   $109.76   $109.75   $109.80  
  Purchase #5 $208.59   4.740%   $218.4772   $218.48   $218.50   $218.50  
  Purchase #6 $123.33   10.608%   $136.4128   $136.41   $136.40   $136.40  
  Purchase #7 $157.78   11.168%   $175.4009   $175.40   $175.40   $175.40  
  7 purchase totals = $916.22       $997.5343   $997.54   $997.50   $997.60