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	$139.89	6.645%	$149.1857	$149.19	$149.20	$149.20
Purchase #2	$37.51	8.556%	$40.7194	$40.72	$40.70	$40.70
Purchase #3	$55.31	7.574%	$59.4992	$59.50	$59.50	$59.50
Purchase #4	$198.34	12.505%	$223.1424	$223.14	$223.15	$223.10
Purchase #5	$18.96	10.407%	$20.9332	$20.93	$20.95	$20.90
Purchase #6	$142.54	10.304%	$157.2273	$157.23	$157.25	$157.20
Purchase #7	$221.91	9.206%	$242.339	$242.34	$242.35	$242.30
7 purchase totals =	$814.46		$893.0462	$893.05	$893.10	$892.90