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	$173.78	8.277%	$188.1638	$188.16	$188.15	$188.20
Purchase #2	$229.83	6.106%	$243.8634	$243.86	$243.85	$243.90
Purchase #3	$10.57	12.549%	$11.8964	$11.90	$11.90	$11.90
Purchase #4	$141.28	6.762%	$150.8334	$150.83	$150.85	$150.80
Purchase #5	$213.26	8.346%	$231.0587	$231.06	$231.05	$231.10
Purchase #6	$140.98	3.849%	$146.4063	$146.41	$146.40	$146.40
Purchase #7	$223.95	11.638%	$250.0133	$250.01	$250.00	$250.00
7 purchase totals =	$1,133.65		$1,222.2353	$1,222.23	$1,222.20	$1,222.30