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	$125.69	13.187%	$142.2647	$142.26	$142.25	$142.30
Purchase #2	$231.32	11.731%	$258.4561	$258.46	$258.45	$258.50
Purchase #3	$212.97	5.249%	$224.1488	$224.15	$224.15	$224.10
Purchase #4	$59.31	10.557%	$65.5714	$65.57	$65.55	$65.60
Purchase #5	$154.54	11.179%	$171.816	$171.82	$171.80	$171.80
Purchase #6	$5.25	4.743%	$5.499	$5.50	$5.50	$5.50
Purchase #7	$36.89	4.749%	$38.6419	$38.64	$38.65	$38.60
7 purchase totals =	$825.97		$906.3979	$906.40	$906.35	$906.40