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	$128.34	8.740%	$139.5569	$139.56	$139.55	$139.60
Purchase #2	$249.57	5.320%	$262.8471	$262.85	$262.85	$262.80
Purchase #3	$53.46	3.687%	$55.4311	$55.43	$55.45	$55.40
Purchase #4	$155.58	10.657%	$172.1602	$172.16	$172.15	$172.20
Purchase #5	$137.98	10.746%	$152.8073	$152.81	$152.80	$152.80
Purchase #6	$18.61	3.384%	$19.2398	$19.24	$19.25	$19.20
Purchase #7	$180.76	7.690%	$194.6604	$194.66	$194.65	$194.70
7 purchase totals =	$924.30		$996.7028	$996.71	$996.70	$996.70