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	$21.86	4.815%	$22.9126	$22.91	$22.90	$22.90
Purchase #2	$36.30	3.209%	$37.4649	$37.46	$37.45	$37.50
Purchase #3	$89.37	12.750%	$100.7647	$100.76	$100.75	$100.80
Purchase #4	$192.71	8.310%	$208.7242	$208.72	$208.70	$208.70
Purchase #5	$41.41	3.139%	$42.7099	$42.71	$42.70	$42.70
Purchase #6	$234.89	13.618%	$266.8773	$266.88	$266.90	$266.90
Purchase #7	$249.69	6.359%	$265.5678	$265.57	$265.55	$265.60
7 purchase totals =	$866.23		$945.0214	$945.01	$944.95	$945.10