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	$65.68	3.111%	$67.7233	$67.72	$67.70	$67.70
Purchase #2	$156.62	12.309%	$175.8984	$175.90	$175.90	$175.90
Purchase #3	$69.61	13.132%	$78.7512	$78.75	$78.75	$78.80
Purchase #4	$124.79	5.865%	$132.1089	$132.11	$132.10	$132.10
Purchase #5	$12.52	3.202%	$12.9209	$12.92	$12.90	$12.90
Purchase #6	$223.97	9.435%	$245.1016	$245.10	$245.10	$245.10
Purchase #7	$70.51	13.517%	$80.0408	$80.04	$80.05	$80.00
7 purchase totals =	$723.70		$792.5451	$792.54	$792.50	$792.50