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	$243.57	11.294%	$271.0788	$271.08	$271.10	$271.10
Purchase #2	$237.80	11.377%	$264.8545	$264.85	$264.85	$264.90
Purchase #3	$175.47	9.133%	$191.4957	$191.50	$191.50	$191.50
Purchase #4	$71.43	13.244%	$80.8902	$80.89	$80.90	$80.90
Purchase #5	$115.52	8.107%	$124.8852	$124.89	$124.90	$124.90
Purchase #6	$134.30	3.389%	$138.8514	$138.85	$138.85	$138.90
Purchase #7	$161.37	6.379%	$171.6638	$171.66	$171.65	$171.70
7 purchase totals =	$1,139.46		$1,243.7196	$1,243.72	$1,243.75	$1,243.90