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	$209.94	6.488%	$223.5609	$223.56	$223.55	$223.60
Purchase #2	$88.87	8.423%	$96.3555	$96.36	$96.35	$96.40
Purchase #3	$72.67	8.174%	$78.61	$78.61	$78.60	$78.60
Purchase #4	$147.97	8.168%	$160.0562	$160.06	$160.05	$160.10
Purchase #5	$170.59	5.219%	$179.4931	$179.49	$179.50	$179.50
Purchase #6	$56.85	13.381%	$64.4571	$64.46	$64.45	$64.50
Purchase #7	$249.75	11.299%	$277.9693	$277.97	$277.95	$278.00
7 purchase totals =	$996.64		$1,080.5021	$1,080.51	$1,080.45	$1,080.70