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	$163.85	3.387%	$169.3996	$169.40	$169.40	$169.40
Purchase #2	$58.88	3.244%	$60.7901	$60.79	$60.80	$60.80
Purchase #3	$82.40	10.228%	$90.8279	$90.83	$90.85	$90.80
Purchase #4	$24.46	7.219%	$26.2258	$26.23	$26.25	$26.20
Purchase #5	$79.64	13.183%	$90.1389	$90.14	$90.15	$90.10
Purchase #6	$211.49	10.547%	$233.7959	$233.80	$233.80	$233.80
Purchase #7	$222.55	12.460%	$250.2797	$250.28	$250.30	$250.30
7 purchase totals =	$843.27		$921.4579	$921.47	$921.55	$921.40