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	$243.78	4.559%	$254.8939	$254.89	$254.90	$254.90
Purchase #2	$164.36	10.664%	$181.8874	$181.89	$181.90	$181.90
Purchase #3	$166.64	5.443%	$175.7102	$175.71	$175.70	$175.70
Purchase #4	$30.64	9.412%	$33.5238	$33.52	$33.50	$33.50
Purchase #5	$85.53	12.496%	$96.2178	$96.22	$96.20	$96.20
Purchase #6	$164.98	6.547%	$175.7812	$175.78	$175.80	$175.80
Purchase #7	$52.82	3.480%	$54.6581	$54.66	$54.65	$54.70
7 purchase totals =	$908.75		$972.6724	$972.67	$972.65	$972.70