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	$85.84	3.869%	$89.1611	$89.16	$89.15	$89.20
Purchase #2	$95.50	4.456%	$99.7555	$99.76	$99.75	$99.80
Purchase #3	$228.86	6.466%	$243.6581	$243.66	$243.65	$243.70
Purchase #4	$168.66	5.839%	$178.5081	$178.51	$178.50	$178.50
Purchase #5	$200.40	4.843%	$210.1054	$210.11	$210.10	$210.10
Purchase #6	$228.71	8.596%	$248.3699	$248.37	$248.35	$248.40
Purchase #7	$115.62	12.778%	$130.3939	$130.39	$130.40	$130.40
7 purchase totals =	$1,123.59		$1,199.9520	$1,199.96	$1,199.90	$1,200.10