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	$23.74	5.868%	$25.1331	$25.13	$25.15	$25.10
Purchase #2	$5.88	10.153%	$6.477	$6.48	$6.50	$6.50
Purchase #3	$145.72	12.764%	$164.3197	$164.32	$164.30	$164.30
Purchase #4	$24.51	9.689%	$26.8848	$26.88	$26.90	$26.90
Purchase #5	$36.76	4.765%	$38.5116	$38.51	$38.50	$38.50
Purchase #6	$68.71	13.273%	$77.8299	$77.83	$77.85	$77.80
Purchase #7	$206.69	7.560%	$222.3158	$222.32	$222.30	$222.30
7 purchase totals =	$512.01		$561.4719	$561.47	$561.50	$561.40