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	$159.59	11.727%	$178.3051	$178.31	$178.30	$178.30
Purchase #2	$124.99	11.354%	$139.1814	$139.18	$139.20	$139.20
Purchase #3	$54.39	7.272%	$58.3452	$58.35	$58.35	$58.30
Purchase #4	$140.89	13.452%	$159.8425	$159.84	$159.85	$159.80
Purchase #5	$168.40	8.592%	$182.8689	$182.87	$182.85	$182.90
Purchase #6	$203.73	3.739%	$211.3475	$211.35	$211.35	$211.30
Purchase #7	$165.29	9.787%	$181.4669	$181.47	$181.45	$181.50
7 purchase totals =	$1,017.28		$1,111.3575	$1,111.37	$1,111.35	$1,111.30