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	$50.58	10.525%	$55.9035	$55.90	$55.90	$55.90
Purchase #2	$144.57	13.822%	$164.5525	$164.55	$164.55	$164.60
Purchase #3	$231.55	8.265%	$250.6876	$250.69	$250.70	$250.70
Purchase #4	$89.61	8.814%	$97.5082	$97.51	$97.50	$97.50
Purchase #5	$17.31	5.765%	$18.3079	$18.31	$18.30	$18.30
Purchase #6	$111.96	11.567%	$124.9104	$124.91	$124.90	$124.90
Purchase #7	$178.37	11.513%	$198.9057	$198.91	$198.90	$198.90
7 purchase totals =	$823.95		$910.7758	$910.78	$910.75	$910.80