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	$102.36	3.110%	$105.5434	$105.54	$105.55	$105.50
Purchase #2	$42.28	6.447%	$45.0058	$45.01	$45.00	$45.00
Purchase #3	$62.74	6.247%	$66.6594	$66.66	$66.65	$66.70
Purchase #4	$18.57	7.469%	$19.957	$19.96	$19.95	$20.00
Purchase #5	$141.70	11.144%	$157.491	$157.49	$157.50	$157.50
Purchase #6	$169.71	7.554%	$182.5299	$182.53	$182.55	$182.50
Purchase #7	$203.95	9.237%	$222.7889	$222.79	$222.80	$222.80
7 purchase totals =	$741.31		$799.9754	$799.98	$800.00	$800.00