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	$36.29	10.588%	$40.1324	$40.13	$40.15	$40.10
Purchase #2	$248.83	6.292%	$264.4864	$264.49	$264.50	$264.50
Purchase #3	$148.76	4.779%	$155.8692	$155.87	$155.85	$155.90
Purchase #4	$42.84	12.585%	$48.2314	$48.23	$48.25	$48.20
Purchase #5	$147.29	12.662%	$165.9399	$165.94	$165.95	$165.90
Purchase #6	$104.95	9.700%	$115.1302	$115.13	$115.15	$115.10
Purchase #7	$177.39	6.276%	$188.523	$188.52	$188.50	$188.50
7 purchase totals =	$906.35		$978.3125	$978.31	$978.35	$978.20