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	$79.75	10.470%	$88.0998	$88.10	$88.10	$88.10
Purchase #2	$87.29	6.428%	$92.901	$92.90	$92.90	$92.90
Purchase #3	$229.46	9.414%	$251.0614	$251.06	$251.05	$251.10
Purchase #4	$195.40	10.689%	$216.2863	$216.29	$216.30	$216.30
Purchase #5	$100.79	4.711%	$105.5382	$105.54	$105.55	$105.50
Purchase #6	$26.97	3.454%	$27.9015	$27.90	$27.90	$27.90
Purchase #7	$63.95	5.512%	$67.4749	$67.47	$67.45	$67.50
7 purchase totals =	$783.61		$849.2631	$849.26	$849.25	$849.30