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	$27.64	5.844%	$29.2553	$29.26	$29.25	$29.30
Purchase #2	$210.32	7.179%	$225.4189	$225.42	$225.40	$225.40
Purchase #3	$74.89	13.613%	$85.0848	$85.08	$85.10	$85.10
Purchase #4	$53.53	11.249%	$59.5516	$59.55	$59.55	$59.60
Purchase #5	$208.59	4.540%	$218.06	$218.06	$218.05	$218.10
Purchase #6	$174.55	8.378%	$189.1738	$189.17	$189.15	$189.20
Purchase #7	$109.34	11.388%	$121.7916	$121.79	$121.80	$121.80
7 purchase totals =	$858.86		$928.3360	$928.33	$928.30	$928.50