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	$68.56	5.515%	$72.3411	$72.34	$72.35	$72.30
Purchase #2	$123.88	12.513%	$139.3811	$139.38	$139.40	$139.40
Purchase #3	$224.78	13.181%	$254.4083	$254.41	$254.40	$254.40
Purchase #4	$137.32	6.192%	$145.8229	$145.82	$145.80	$145.80
Purchase #5	$237.94	11.182%	$264.5465	$264.55	$264.55	$264.50
Purchase #6	$244.76	12.494%	$275.3403	$275.34	$275.35	$275.30
Purchase #7	$23.82	12.814%	$26.8723	$26.87	$26.85	$26.90
7 purchase totals =	$1,061.06		$1,178.7125	$1,178.71	$1,178.70	$1,178.60