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	$192.32	10.535%	$212.5809	$212.58	$212.60	$212.60
Purchase #2	$211.57	10.317%	$233.3977	$233.40	$233.40	$233.40
Purchase #3	$24.96	3.865%	$25.9247	$25.92	$25.90	$25.90
Purchase #4	$140.38	10.788%	$155.5242	$155.52	$155.50	$155.50
Purchase #5	$92.94	7.121%	$99.5583	$99.56	$99.55	$99.60
Purchase #6	$79.73	10.320%	$87.9581	$87.96	$87.95	$88.00
Purchase #7	$42.69	3.386%	$44.1355	$44.14	$44.15	$44.10
7 purchase totals =	$784.59		$859.0794	$859.08	$859.05	$859.10