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	$150.29	12.666%	$169.3257	$169.33	$169.35	$169.30
Purchase #2	$200.77	4.600%	$210.0054	$210.01	$210.00	$210.00
Purchase #3	$44.48	13.200%	$50.3514	$50.35	$50.35	$50.40
Purchase #4	$194.43	11.213%	$216.2314	$216.23	$216.25	$216.20
Purchase #5	$168.72	7.764%	$181.8194	$181.82	$181.80	$181.80
Purchase #6	$17.69	13.833%	$20.1371	$20.14	$20.15	$20.10
Purchase #7	$48.51	9.403%	$53.0714	$53.07	$53.05	$53.10
7 purchase totals =	$824.89		$900.9418	$900.95	$900.95	$900.90