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	$18.54	9.724%	$20.3428	$20.34	$20.35	$20.30
Purchase #2	$143.31	3.197%	$147.8916	$147.89	$147.90	$147.90
Purchase #3	$250.41	9.513%	$274.2315	$274.23	$274.25	$274.20
Purchase #4	$56.91	13.619%	$64.6606	$64.66	$64.65	$64.70
Purchase #5	$95.38	4.579%	$99.7475	$99.75	$99.75	$99.70
Purchase #6	$50.73	7.275%	$54.4206	$54.42	$54.40	$54.40
Purchase #7	$217.31	8.617%	$236.0356	$236.04	$236.05	$236.00
7 purchase totals =	$832.59		$897.3302	$897.33	$897.35	$897.20