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	$242.72	11.265%	$270.0624	$270.06	$270.05	$270.10
Purchase #2	$228.83	11.247%	$254.5665	$254.57	$254.55	$254.60
Purchase #3	$84.80	3.740%	$87.9715	$87.97	$87.95	$88.00
Purchase #4	$223.94	5.161%	$235.4975	$235.50	$235.50	$235.50
Purchase #5	$38.38	10.497%	$42.4087	$42.41	$42.40	$42.40
Purchase #6	$86.54	3.204%	$89.3127	$89.31	$89.30	$89.30
Purchase #7	$38.33	6.262%	$40.7302	$40.73	$40.75	$40.70
7 purchase totals =	$943.54		$1,020.5495	$1,020.55	$1,020.50	$1,020.60