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	$153.27	6.490%	$163.2172	$163.22	$163.20	$163.20
Purchase #2	$82.96	8.239%	$89.7951	$89.80	$89.80	$89.80
Purchase #3	$109.50	5.320%	$115.3254	$115.33	$115.35	$115.30
Purchase #4	$109.71	12.681%	$123.6223	$123.62	$123.60	$123.60
Purchase #5	$106.46	11.427%	$118.6252	$118.63	$118.65	$118.60
Purchase #6	$175.78	6.568%	$187.3252	$187.33	$187.35	$187.30
Purchase #7	$137.84	4.728%	$144.3571	$144.36	$144.35	$144.40
7 purchase totals =	$875.52		$942.2675	$942.29	$942.30	$942.20