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	$228.37	6.749%	$243.7827	$243.78	$243.80	$243.80
Purchase #2	$213.88	3.820%	$222.0502	$222.05	$222.05	$222.10
Purchase #3	$36.90	9.514%	$40.4107	$40.41	$40.40	$40.40
Purchase #4	$141.73	13.693%	$161.1371	$161.14	$161.15	$161.10
Purchase #5	$129.82	12.204%	$145.6632	$145.66	$145.65	$145.70
Purchase #6	$31.77	3.436%	$32.8616	$32.86	$32.85	$32.90
Purchase #7	$142.62	9.585%	$156.2901	$156.29	$156.30	$156.30
7 purchase totals =	$925.09		$1,002.1956	$1,002.19	$1,002.20	$1,002.30