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	$172.71	13.722%	$196.4093	$196.41	$196.40	$196.40
Purchase #2	$61.80	9.146%	$67.4522	$67.45	$67.45	$67.50
Purchase #3	$97.48	5.519%	$102.8599	$102.86	$102.85	$102.90
Purchase #4	$153.89	9.617%	$168.6896	$168.69	$168.70	$168.70
Purchase #5	$232.40	7.801%	$250.5295	$250.53	$250.55	$250.50
Purchase #6	$43.53	4.115%	$45.3213	$45.32	$45.30	$45.30
Purchase #7	$243.79	6.854%	$260.4994	$260.50	$260.50	$260.50
7 purchase totals =	$1,005.60		$1,091.7612	$1,091.76	$1,091.75	$1,091.80