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	$59.33	13.323%	$67.2345	$67.23	$67.25	$67.20
Purchase #2	$201.75	10.270%	$222.4697	$222.47	$222.45	$222.50
Purchase #3	$20.91	9.297%	$22.854	$22.85	$22.85	$22.90
Purchase #4	$18.49	13.156%	$20.9225	$20.92	$20.90	$20.90
Purchase #5	$97.57	6.513%	$103.9247	$103.92	$103.90	$103.90
Purchase #6	$86.35	5.670%	$91.246	$91.25	$91.25	$91.20
Purchase #7	$236.25	5.614%	$249.5131	$249.51	$249.50	$249.50
7 purchase totals =	$720.65		$778.1645	$778.15	$778.10	$778.10