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	$110.90	12.517%	$124.7814	$124.78	$124.80	$124.80
Purchase #2	$159.35	6.310%	$169.405	$169.41	$169.40	$169.40
Purchase #3	$35.43	9.467%	$38.7842	$38.78	$38.80	$38.80
Purchase #4	$141.33	7.730%	$152.2548	$152.25	$152.25	$152.30
Purchase #5	$40.37	4.464%	$42.1721	$42.17	$42.15	$42.20
Purchase #6	$36.92	9.749%	$40.5193	$40.52	$40.50	$40.50
Purchase #7	$226.75	10.861%	$251.3773	$251.38	$251.40	$251.40
7 purchase totals =	$751.05		$819.2941	$819.29	$819.30	$819.40