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	$28.37	12.414%	$31.8919	$31.89	$31.90	$31.90
Purchase #2	$133.83	13.814%	$152.3173	$152.32	$152.30	$152.30
Purchase #3	$120.34	6.167%	$127.7614	$127.76	$127.75	$127.80
Purchase #4	$201.50	7.506%	$216.6246	$216.62	$216.60	$216.60
Purchase #5	$214.81	13.143%	$243.0425	$243.04	$243.05	$243.00
Purchase #6	$221.64	8.297%	$240.0295	$240.03	$240.05	$240.00
Purchase #7	$54.39	10.630%	$60.1717	$60.17	$60.15	$60.20
7 purchase totals =	$974.88		$1,071.8389	$1,071.83	$1,071.80	$1,071.80