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	$249.86	8.254%	$270.4834	$270.48	$270.50	$270.50
Purchase #2	$241.89	9.263%	$264.2963	$264.30	$264.30	$264.30
Purchase #3	$197.46	12.702%	$222.5414	$222.54	$222.55	$222.50
Purchase #4	$221.39	11.801%	$247.5162	$247.52	$247.50	$247.50
Purchase #5	$119.41	4.700%	$125.0223	$125.02	$125.00	$125.00
Purchase #6	$79.54	12.755%	$89.6853	$89.69	$89.70	$89.70
Purchase #7	$236.60	7.461%	$254.2527	$254.25	$254.25	$254.30
7 purchase totals =	$1,346.15		$1,473.7976	$1,473.80	$1,473.80	$1,473.80