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	$136.52	7.588%	$146.8791	$146.88	$146.90	$146.90
Purchase #2	$220.66	13.417%	$250.266	$250.27	$250.25	$250.30
Purchase #3	$39.47	10.417%	$43.5816	$43.58	$43.60	$43.60
Purchase #4	$5.86	3.405%	$6.0595	$6.06	$6.05	$6.10
Purchase #5	$100.62	8.634%	$109.3075	$109.31	$109.30	$109.30
Purchase #6	$156.36	3.739%	$162.2063	$162.21	$162.20	$162.20
Purchase #7	$31.39	6.279%	$33.361	$33.36	$33.35	$33.40
7 purchase totals =	$690.88		$751.6610	$751.67	$751.65	$751.80