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	$128.44	6.614%	$136.935	$136.94	$136.95	$136.90
Purchase #2	$80.75	11.341%	$89.9079	$89.91	$89.90	$89.90
Purchase #3	$157.77	9.867%	$173.3372	$173.34	$173.35	$173.30
Purchase #4	$115.94	12.537%	$130.4754	$130.48	$130.50	$130.50
Purchase #5	$243.59	10.768%	$269.8198	$269.82	$269.80	$269.80
Purchase #6	$249.84	10.720%	$276.6228	$276.62	$276.60	$276.60
Purchase #7	$176.88	11.328%	$196.917	$196.92	$196.90	$196.90
7 purchase totals =	$1,153.21		$1,274.0151	$1,274.03	$1,274.00	$1,273.90