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	$28.26	7.329%	$30.3312	$30.33	$30.35	$30.30
Purchase #2	$56.64	5.343%	$59.6663	$59.67	$59.65	$59.70
Purchase #3	$104.67	11.332%	$116.5312	$116.53	$116.55	$116.50
Purchase #4	$250.91	3.164%	$258.8488	$258.85	$258.85	$258.80
Purchase #5	$155.42	10.207%	$171.2837	$171.28	$171.30	$171.30
Purchase #6	$209.50	13.717%	$238.2371	$238.24	$238.25	$238.20
Purchase #7	$171.55	10.203%	$189.0532	$189.05	$189.05	$189.10
7 purchase totals =	$976.95		$1,063.9515	$1,063.95	$1,064.00	$1,063.90