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	$234.48	12.544%	$263.8932	$263.89	$263.90	$263.90
Purchase #2	$57.36	9.603%	$62.8683	$62.87	$62.85	$62.90
Purchase #3	$204.68	3.720%	$212.2941	$212.29	$212.30	$212.30
Purchase #4	$163.92	3.801%	$170.1506	$170.15	$170.15	$170.20
Purchase #5	$91.77	8.849%	$99.8907	$99.89	$99.90	$99.90
Purchase #6	$86.84	3.802%	$90.1417	$90.14	$90.15	$90.10
Purchase #7	$170.32	12.734%	$192.0085	$192.01	$192.00	$192.00
7 purchase totals =	$1,009.37		$1,091.2471	$1,091.24	$1,091.25	$1,091.30