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	$50.32	6.378%	$53.5294	$53.53	$53.55	$53.50
Purchase #2	$188.68	4.350%	$196.8876	$196.89	$196.90	$196.90
Purchase #3	$7.30	13.537%	$8.2882	$8.29	$8.30	$8.30
Purchase #4	$74.65	5.507%	$78.761	$78.76	$78.75	$78.80
Purchase #5	$174.72	9.365%	$191.0825	$191.08	$191.10	$191.10
Purchase #6	$95.94	11.451%	$106.9261	$106.93	$106.95	$106.90
Purchase #7	$110.36	12.381%	$124.0237	$124.02	$124.00	$124.00
7 purchase totals =	$701.97		$759.4985	$759.50	$759.55	$759.50