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	$175.59	3.121%	$181.0702	$181.07	$181.05	$181.10
Purchase #2	$174.54	7.580%	$187.7701	$187.77	$187.75	$187.80
Purchase #3	$49.69	10.761%	$55.0371	$55.04	$55.05	$55.00
Purchase #4	$83.55	6.534%	$89.0092	$89.01	$89.00	$89.00
Purchase #5	$165.46	9.613%	$181.3657	$181.37	$181.35	$181.40
Purchase #6	$95.90	12.459%	$107.8482	$107.85	$107.85	$107.80
Purchase #7	$35.40	12.550%	$39.8427	$39.84	$39.85	$39.80
7 purchase totals =	$780.13		$841.9432	$841.95	$841.90	$841.90