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	$33.67	9.710%	$36.9394	$36.94	$36.95	$36.90
Purchase #2	$63.86	6.340%	$67.9087	$67.91	$67.90	$67.90
Purchase #3	$28.98	11.520%	$32.3185	$32.32	$32.30	$32.30
Purchase #4	$172.90	7.414%	$185.7188	$185.72	$185.70	$185.70
Purchase #5	$138.39	8.456%	$150.0923	$150.09	$150.10	$150.10
Purchase #6	$209.73	3.594%	$217.2677	$217.27	$217.25	$217.30
Purchase #7	$143.87	7.748%	$155.017	$155.02	$155.00	$155.00
7 purchase totals =	$791.40		$845.2624	$845.27	$845.20	$845.20