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	$131.74	5.619%	$139.1425	$139.14	$139.15	$139.10
Purchase #2	$135.81	12.576%	$152.8895	$152.89	$152.90	$152.90
Purchase #3	$225.37	7.499%	$242.2705	$242.27	$242.25	$242.30
Purchase #4	$243.59	13.295%	$275.9753	$275.98	$276.00	$276.00
Purchase #5	$10.28	4.837%	$10.7772	$10.78	$10.80	$10.80
Purchase #6	$127.47	10.867%	$141.3222	$141.32	$141.30	$141.30
Purchase #7	$203.43	5.520%	$214.6593	$214.66	$214.65	$214.70
7 purchase totals =	$1,077.69		$1,177.0365	$1,177.04	$1,177.05	$1,177.10