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	$46.49	10.158%	$51.2125	$51.21	$51.20	$51.20
Purchase #2	$148.95	10.703%	$164.8921	$164.89	$164.90	$164.90
Purchase #3	$94.26	5.311%	$99.2661	$99.27	$99.25	$99.30
Purchase #4	$88.68	6.644%	$94.5719	$94.57	$94.55	$94.60
Purchase #5	$83.61	12.555%	$94.1072	$94.11	$94.10	$94.10
Purchase #6	$179.28	3.321%	$185.2339	$185.23	$185.25	$185.20
Purchase #7	$232.86	7.690%	$250.7669	$250.77	$250.75	$250.80
7 purchase totals =	$874.13		$940.0506	$940.05	$940.00	$940.10