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 $190.28   6.824%   $203.2647   $203.26   $203.25   $203.30  
  Purchase #2 $34.76   3.621%   $36.0187   $36.02   $36.00   $36.00  
  Purchase #3 $238.80   13.747%   $271.6278   $271.63   $271.65   $271.60  
  Purchase #4 $40.43   12.862%   $45.6301   $45.63   $45.65   $45.60  
  Purchase #5 $81.99   9.778%   $90.007   $90.01   $90.00   $90.00  
  Purchase #6 $167.87   9.370%   $183.5994   $183.60   $183.60   $183.60  
  Purchase #7 $230.86   6.767%   $246.4823   $246.48   $246.50   $246.50  
  7 purchase totals = $984.99       $1,076.6300   $1,076.63   $1,076.65   $1,076.60