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	$194.62	12.603%	$219.148	$219.15	$219.15	$219.10
Purchase #2	$181.37	10.520%	$200.4501	$200.45	$200.45	$200.50
Purchase #3	$87.33	12.788%	$98.4978	$98.50	$98.50	$98.50
Purchase #4	$66.65	10.743%	$73.8102	$73.81	$73.80	$73.80
Purchase #5	$83.90	9.288%	$91.6926	$91.69	$91.70	$91.70
Purchase #6	$28.32	12.444%	$31.8441	$31.84	$31.85	$31.80
Purchase #7	$79.37	5.652%	$83.856	$83.86	$83.85	$83.90
7 purchase totals =	$721.56		$799.2988	$799.30	$799.30	$799.30