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	$75.91	4.769%	$79.5301	$79.53	$79.55	$79.50
Purchase #2	$51.81	6.724%	$55.2937	$55.29	$55.30	$55.30
Purchase #3	$141.43	4.110%	$147.2428	$147.24	$147.25	$147.20
Purchase #4	$39.62	7.176%	$42.4631	$42.46	$42.45	$42.50
Purchase #5	$153.74	11.414%	$171.2879	$171.29	$171.30	$171.30
Purchase #6	$211.60	5.399%	$223.0243	$223.02	$223.00	$223.00
Purchase #7	$50.90	8.285%	$55.1171	$55.12	$55.10	$55.10
7 purchase totals =	$725.01		$773.9590	$773.95	$773.95	$773.90