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	$67.70	11.415%	$75.428	$75.43	$75.45	$75.40
Purchase #2	$40.47	6.824%	$43.2317	$43.23	$43.25	$43.20
Purchase #3	$216.32	8.868%	$235.5033	$235.50	$235.50	$235.50
Purchase #4	$70.29	12.160%	$78.8373	$78.84	$78.85	$78.80
Purchase #5	$159.83	5.194%	$168.1316	$168.13	$168.15	$168.10
Purchase #6	$79.62	12.576%	$89.633	$89.63	$89.65	$89.60
Purchase #7	$71.30	11.147%	$79.2478	$79.25	$79.25	$79.20
7 purchase totals =	$705.53		$770.0127	$770.01	$770.10	$769.80