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	$50.67	13.454%	$57.4871	$57.49	$57.50	$57.50
Purchase #2	$149.30	4.140%	$155.481	$155.48	$155.50	$155.50
Purchase #3	$89.78	12.350%	$100.8678	$100.87	$100.85	$100.90
Purchase #4	$23.90	4.800%	$25.0472	$25.05	$25.05	$25.00
Purchase #5	$176.77	11.518%	$197.1304	$197.13	$197.15	$197.10
Purchase #6	$149.77	8.440%	$162.4106	$162.41	$162.40	$162.40
Purchase #7	$102.89	8.793%	$111.9371	$111.94	$111.95	$111.90
7 purchase totals =	$743.08		$810.3612	$810.37	$810.40	$810.30