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	$62.74	11.808%	$70.1483	$70.15	$70.15	$70.10
Purchase #2	$209.74	5.516%	$221.3093	$221.31	$221.30	$221.30
Purchase #3	$166.59	11.303%	$185.4197	$185.42	$185.40	$185.40
Purchase #4	$29.87	13.508%	$33.9048	$33.90	$33.90	$33.90
Purchase #5	$233.31	3.260%	$240.9159	$240.92	$240.90	$240.90
Purchase #6	$85.51	13.187%	$96.7862	$96.79	$96.80	$96.80
Purchase #7	$6.70	12.107%	$7.5112	$7.51	$7.50	$7.50
7 purchase totals =	$794.46		$855.9954	$856.00	$855.95	$855.90