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	$250.32	8.872%	$272.5284	$272.53	$272.55	$272.50
Purchase #2	$64.51	7.661%	$69.4521	$69.45	$69.45	$69.50
Purchase #3	$147.52	3.201%	$152.2421	$152.24	$152.25	$152.20
Purchase #4	$56.78	4.168%	$59.1466	$59.15	$59.15	$59.10
Purchase #5	$79.38	7.369%	$85.2295	$85.23	$85.25	$85.20
Purchase #6	$13.40	4.789%	$14.0417	$14.04	$14.05	$14.00
Purchase #7	$127.43	10.706%	$141.0727	$141.07	$141.05	$141.10
7 purchase totals =	$739.34		$793.7131	$793.71	$793.75	$793.60