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	$40.29	5.808%	$42.63	$42.63	$42.65	$42.60
Purchase #2	$90.71	6.479%	$96.5871	$96.59	$96.60	$96.60
Purchase #3	$165.97	3.562%	$171.8819	$171.88	$171.90	$171.90
Purchase #4	$202.30	11.727%	$226.0237	$226.02	$226.00	$226.00
Purchase #5	$99.71	5.150%	$104.8451	$104.85	$104.85	$104.80
Purchase #6	$53.63	5.318%	$56.482	$56.48	$56.50	$56.50
Purchase #7	$149.70	4.306%	$156.1461	$156.15	$156.15	$156.10
7 purchase totals =	$802.31		$854.5959	$854.60	$854.65	$854.50