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	$188.50	6.568%	$200.8807	$200.88	$200.90	$200.90
Purchase #2	$61.34	11.380%	$68.3205	$68.32	$68.30	$68.30
Purchase #3	$124.25	9.834%	$136.4687	$136.47	$136.45	$136.50
Purchase #4	$10.60	13.670%	$12.049	$12.05	$12.05	$12.00
Purchase #5	$179.57	6.294%	$190.8721	$190.87	$190.85	$190.90
Purchase #6	$31.29	6.165%	$33.219	$33.22	$33.20	$33.20
Purchase #7	$249.62	13.579%	$283.5159	$283.52	$283.50	$283.50
7 purchase totals =	$845.17		$925.3259	$925.33	$925.25	$925.30