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	$174.79	7.820%	$188.4586	$188.46	$188.45	$188.50
Purchase #2	$129.70	12.210%	$145.5364	$145.54	$145.55	$145.50
Purchase #3	$108.51	11.223%	$120.6881	$120.69	$120.70	$120.70
Purchase #4	$228.98	11.442%	$255.1799	$255.18	$255.20	$255.20
Purchase #5	$72.34	8.119%	$78.2133	$78.21	$78.20	$78.20
Purchase #6	$83.90	6.378%	$89.2511	$89.25	$89.25	$89.30
Purchase #7	$50.31	9.478%	$55.0784	$55.08	$55.10	$55.10
7 purchase totals =	$848.53		$932.4058	$932.41	$932.45	$932.50