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	$42.44	8.119%	$45.8857	$45.89	$45.90	$45.90
Purchase #2	$64.33	3.600%	$66.6459	$66.65	$66.65	$66.60
Purchase #3	$245.99	3.847%	$255.4532	$255.45	$255.45	$255.50
Purchase #4	$73.63	12.570%	$82.8853	$82.89	$82.90	$82.90
Purchase #5	$248.83	11.129%	$276.5223	$276.52	$276.50	$276.50
Purchase #6	$109.67	9.842%	$120.4637	$120.46	$120.45	$120.50
Purchase #7	$9.62	5.523%	$10.1513	$10.15	$10.15	$10.20
7 purchase totals =	$794.51		$858.0074	$858.01	$858.00	$858.10