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	$171.33	10.631%	$189.5441	$189.54	$189.55	$189.50
Purchase #2	$204.96	12.173%	$229.9098	$229.91	$229.90	$229.90
Purchase #3	$159.78	6.125%	$169.5665	$169.57	$169.55	$169.60
Purchase #4	$197.51	8.510%	$214.3181	$214.32	$214.30	$214.30
Purchase #5	$234.67	9.301%	$256.4967	$256.50	$256.50	$256.50
Purchase #6	$175.90	5.164%	$184.9835	$184.98	$185.00	$185.00
Purchase #7	$36.72	13.778%	$41.7793	$41.78	$41.80	$41.80
7 purchase totals =	$1,180.87		$1,286.5980	$1,286.60	$1,286.60	$1,286.60