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	$76.74	5.851%	$81.2301	$81.23	$81.25	$81.20
Purchase #2	$18.82	3.715%	$19.5192	$19.52	$19.50	$19.50
Purchase #3	$185.90	3.221%	$191.8878	$191.89	$191.90	$191.90
Purchase #4	$65.68	8.716%	$71.4047	$71.40	$71.40	$71.40
Purchase #5	$149.45	12.268%	$167.7845	$167.78	$167.80	$167.80
Purchase #6	$88.57	6.332%	$94.1783	$94.18	$94.20	$94.20
Purchase #7	$155.47	4.270%	$162.1086	$162.11	$162.10	$162.10
7 purchase totals =	$740.63		$788.1132	$788.11	$788.15	$788.10