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	$133.27	5.711%	$140.881	$140.88	$140.90	$140.90
Purchase #2	$99.52	8.365%	$107.8448	$107.84	$107.85	$107.80
Purchase #3	$69.34	3.672%	$71.8862	$71.89	$71.90	$71.90
Purchase #4	$134.76	8.312%	$145.9613	$145.96	$145.95	$146.00
Purchase #5	$106.70	8.631%	$115.9093	$115.91	$115.90	$115.90
Purchase #6	$119.79	9.554%	$131.2347	$131.23	$131.25	$131.20
Purchase #7	$77.88	10.138%	$85.7755	$85.78	$85.80	$85.80
7 purchase totals =	$741.26		$799.4928	$799.49	$799.55	$799.50