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	$119.59	13.323%	$135.523	$135.52	$135.50	$135.50
Purchase #2	$224.78	7.562%	$241.7779	$241.78	$241.80	$241.80
Purchase #3	$146.89	3.722%	$152.3572	$152.36	$152.35	$152.40
Purchase #4	$183.95	3.382%	$190.1712	$190.17	$190.15	$190.20
Purchase #5	$50.33	9.489%	$55.1058	$55.11	$55.10	$55.10
Purchase #6	$42.40	13.461%	$48.1075	$48.11	$48.10	$48.10
Purchase #7	$246.57	7.417%	$264.8581	$264.86	$264.85	$264.90
7 purchase totals =	$1,014.51		$1,087.9007	$1,087.91	$1,087.85	$1,088.00