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	$79.97	7.198%	$85.7262	$85.73	$85.75	$85.70
Purchase #2	$164.89	11.653%	$184.1046	$184.10	$184.10	$184.10
Purchase #3	$128.71	13.666%	$146.2995	$146.30	$146.30	$146.30
Purchase #4	$56.72	6.259%	$60.2701	$60.27	$60.25	$60.30
Purchase #5	$87.48	10.347%	$96.5316	$96.53	$96.55	$96.50
Purchase #6	$28.71	8.853%	$31.2517	$31.25	$31.25	$31.30
Purchase #7	$29.76	12.666%	$33.5294	$33.53	$33.55	$33.50
7 purchase totals =	$576.24		$637.7131	$637.71	$637.75	$637.70