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	$167.42	6.787%	$178.7828	$178.78	$178.80	$178.80
Purchase #2	$148.97	13.700%	$169.3789	$169.38	$169.40	$169.40
Purchase #3	$198.43	12.573%	$223.3786	$223.38	$223.40	$223.40
Purchase #4	$80.35	4.181%	$83.7094	$83.71	$83.70	$83.70
Purchase #5	$155.37	7.701%	$167.335	$167.34	$167.35	$167.30
Purchase #6	$218.92	10.688%	$242.3182	$242.32	$242.30	$242.30
Purchase #7	$75.55	13.378%	$85.6571	$85.66	$85.65	$85.70
7 purchase totals =	$1,045.01		$1,150.5600	$1,150.57	$1,150.60	$1,150.60