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	$166.91	10.177%	$183.8964	$183.90	$183.90	$183.90
Purchase #2	$124.36	7.861%	$134.1359	$134.14	$134.15	$134.10
Purchase #3	$31.88	7.326%	$34.2155	$34.22	$34.20	$34.20
Purchase #4	$39.33	3.131%	$40.5614	$40.56	$40.55	$40.60
Purchase #5	$86.38	5.218%	$90.8873	$90.89	$90.90	$90.90
Purchase #6	$146.72	3.673%	$152.109	$152.11	$152.10	$152.10
Purchase #7	$143.93	3.498%	$148.9647	$148.96	$148.95	$149.00
7 purchase totals =	$739.51		$784.7702	$784.78	$784.75	$784.80