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	$229.81	6.132%	$243.9019	$243.90	$243.90	$243.90
Purchase #2	$14.56	6.561%	$15.5153	$15.52	$15.50	$15.50
Purchase #3	$109.72	4.862%	$115.0546	$115.05	$115.05	$115.10
Purchase #4	$25.58	9.292%	$27.9569	$27.96	$27.95	$28.00
Purchase #5	$136.73	11.441%	$152.3733	$152.37	$152.35	$152.40
Purchase #6	$175.51	5.694%	$185.5035	$185.50	$185.50	$185.50
Purchase #7	$70.88	8.807%	$77.1224	$77.12	$77.10	$77.10
7 purchase totals =	$762.79		$817.4279	$817.42	$817.35	$817.50