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	$47.37	12.764%	$53.4163	$53.42	$53.40	$53.40
Purchase #2	$52.52	11.604%	$58.6144	$58.61	$58.60	$58.60
Purchase #3	$131.48	10.681%	$145.5234	$145.52	$145.50	$145.50
Purchase #4	$120.26	9.163%	$131.2794	$131.28	$131.30	$131.30
Purchase #5	$142.78	11.517%	$159.224	$159.22	$159.20	$159.20
Purchase #6	$191.82	11.104%	$213.1197	$213.12	$213.10	$213.10
Purchase #7	$198.55	6.837%	$212.1249	$212.12	$212.10	$212.10
7 purchase totals =	$884.78		$973.3021	$973.29	$973.20	$973.20