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	$86.58	6.574%	$92.2718	$92.27	$92.25	$92.30
Purchase #2	$70.76	9.187%	$77.2607	$77.26	$77.25	$77.30
Purchase #3	$79.54	4.289%	$82.9515	$82.95	$82.95	$83.00
Purchase #4	$42.74	6.239%	$45.4065	$45.41	$45.40	$45.40
Purchase #5	$41.54	9.392%	$45.4414	$45.44	$45.45	$45.40
Purchase #6	$122.47	12.207%	$137.4199	$137.42	$137.40	$137.40
Purchase #7	$89.33	10.215%	$98.4551	$98.46	$98.45	$98.50
7 purchase totals =	$532.96		$579.2069	$579.21	$579.15	$579.30