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	$165.28	10.531%	$182.6856	$182.69	$182.70	$182.70
Purchase #2	$73.94	13.494%	$83.9175	$83.92	$83.90	$83.90
Purchase #3	$82.90	9.143%	$90.4795	$90.48	$90.50	$90.50
Purchase #4	$211.54	4.412%	$220.8731	$220.87	$220.85	$220.90
Purchase #5	$139.28	5.427%	$146.8387	$146.84	$146.85	$146.80
Purchase #6	$120.90	5.197%	$127.1832	$127.18	$127.20	$127.20
Purchase #7	$227.82	4.560%	$238.2086	$238.21	$238.20	$238.20
7 purchase totals =	$1,021.66		$1,090.1862	$1,090.19	$1,090.20	$1,090.20