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	$165.76	12.239%	$186.0474	$186.05	$186.05	$186.00
Purchase #2	$81.89	9.569%	$89.7261	$89.73	$89.75	$89.70
Purchase #3	$147.93	5.325%	$155.8073	$155.81	$155.80	$155.80
Purchase #4	$81.75	8.417%	$88.6309	$88.63	$88.65	$88.60
Purchase #5	$126.52	8.199%	$136.8934	$136.89	$136.90	$136.90
Purchase #6	$50.33	13.278%	$57.0128	$57.01	$57.00	$57.00
Purchase #7	$65.46	7.293%	$70.234	$70.23	$70.25	$70.20
7 purchase totals =	$719.64		$784.3519	$784.35	$784.40	$784.20