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	$66.77	6.674%	$71.2262	$71.23	$71.25	$71.20
Purchase #2	$51.40	4.108%	$53.5115	$53.51	$53.50	$53.50
Purchase #3	$78.39	3.163%	$80.8695	$80.87	$80.85	$80.90
Purchase #4	$79.89	3.431%	$82.631	$82.63	$82.65	$82.60
Purchase #5	$48.84	7.121%	$52.3179	$52.32	$52.30	$52.30
Purchase #6	$17.33	12.819%	$19.5515	$19.55	$19.55	$19.60
Purchase #7	$133.82	3.272%	$138.1986	$138.20	$138.20	$138.20
7 purchase totals =	$476.44		$498.3062	$498.31	$498.30	$498.30