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	$198.63	10.864%	$220.2092	$220.21	$220.20	$220.20
Purchase #2	$165.32	6.173%	$175.5252	$175.53	$175.55	$175.50
Purchase #3	$158.43	9.108%	$172.8598	$172.86	$172.85	$172.90
Purchase #4	$216.77	12.147%	$243.1011	$243.10	$243.10	$243.10
Purchase #5	$75.28	7.446%	$80.8853	$80.89	$80.90	$80.90
Purchase #6	$82.53	3.489%	$85.4095	$85.41	$85.40	$85.40
Purchase #7	$18.54	6.654%	$19.7737	$19.77	$19.75	$19.80
7 purchase totals =	$915.50		$997.7638	$997.77	$997.75	$997.80