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	$50.73	4.254%	$52.8881	$52.89	$52.90	$52.90
Purchase #2	$147.34	7.456%	$158.3257	$158.33	$158.35	$158.30
Purchase #3	$185.32	5.857%	$196.1742	$196.17	$196.15	$196.20
Purchase #4	$26.56	9.571%	$29.1021	$29.10	$29.10	$29.10
Purchase #5	$140.25	4.851%	$147.0535	$147.05	$147.05	$147.10
Purchase #6	$72.45	13.652%	$82.3409	$82.34	$82.35	$82.30
Purchase #7	$55.56	9.847%	$61.031	$61.03	$61.05	$61.00
7 purchase totals =	$678.21		$726.9155	$726.91	$726.95	$726.90