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	$125.56	13.415%	$142.4039	$142.40	$142.40	$142.40
Purchase #2	$87.75	9.669%	$96.2345	$96.23	$96.25	$96.20
Purchase #3	$82.74	3.822%	$85.9023	$85.90	$85.90	$85.90
Purchase #4	$50.89	11.152%	$56.5653	$56.57	$56.55	$56.60
Purchase #5	$126.87	9.155%	$138.4849	$138.48	$138.50	$138.50
Purchase #6	$52.28	3.424%	$54.0701	$54.07	$54.05	$54.10
Purchase #7	$178.58	7.812%	$192.5307	$192.53	$192.55	$192.50
7 purchase totals =	$704.67		$766.1917	$766.18	$766.20	$766.20