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	$31.90	12.479%	$35.8808	$35.88	$35.90	$35.90
Purchase #2	$192.51	3.334%	$198.9283	$198.93	$198.95	$198.90
Purchase #3	$140.42	7.300%	$150.6707	$150.67	$150.65	$150.70
Purchase #4	$64.49	10.663%	$71.3666	$71.37	$71.35	$71.40
Purchase #5	$178.41	9.867%	$196.0137	$196.01	$196.00	$196.00
Purchase #6	$139.84	11.475%	$155.8866	$155.89	$155.90	$155.90
Purchase #7	$110.86	9.436%	$121.3207	$121.32	$121.30	$121.30
7 purchase totals =	$858.43		$930.0674	$930.07	$930.05	$930.10