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	$104.55	9.307%	$114.2805	$114.28	$114.30	$114.30
Purchase #2	$63.47	6.133%	$67.3626	$67.36	$67.35	$67.40
Purchase #3	$35.76	9.682%	$39.2223	$39.22	$39.20	$39.20
Purchase #4	$247.76	8.178%	$268.0218	$268.02	$268.00	$268.00
Purchase #5	$145.50	4.786%	$152.4636	$152.46	$152.45	$152.50
Purchase #6	$105.58	10.367%	$116.5255	$116.53	$116.55	$116.50
Purchase #7	$82.76	9.130%	$90.316	$90.32	$90.30	$90.30
7 purchase totals =	$785.38		$848.1923	$848.19	$848.15	$848.20