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	$157.47	5.700%	$166.4458	$166.45	$166.45	$166.40
Purchase #2	$59.71	4.506%	$62.4005	$62.40	$62.40	$62.40
Purchase #3	$58.77	11.234%	$65.3722	$65.37	$65.35	$65.40
Purchase #4	$31.65	6.800%	$33.8022	$33.80	$33.80	$33.80
Purchase #5	$16.84	6.776%	$17.9811	$17.98	$18.00	$18.00
Purchase #6	$92.65	4.576%	$96.8897	$96.89	$96.90	$96.90
Purchase #7	$58.90	9.179%	$64.3064	$64.31	$64.30	$64.30
7 purchase totals =	$475.99		$507.1979	$507.20	$507.20	$507.20