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	$249.58	8.566%	$270.959	$270.96	$270.95	$271.00
Purchase #2	$86.85	13.281%	$98.3845	$98.38	$98.40	$98.40
Purchase #3	$196.59	7.460%	$211.2556	$211.26	$211.25	$211.30
Purchase #4	$77.50	10.212%	$85.4143	$85.41	$85.40	$85.40
Purchase #5	$201.51	4.368%	$210.312	$210.31	$210.30	$210.30
Purchase #6	$47.83	13.464%	$54.2698	$54.27	$54.25	$54.30
Purchase #7	$165.83	10.132%	$182.6319	$182.63	$182.65	$182.60
7 purchase totals =	$1,025.69		$1,113.2271	$1,113.22	$1,113.20	$1,113.30