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	$79.55	5.260%	$83.7343	$83.73	$83.75	$83.70
Purchase #2	$102.95	13.700%	$117.0542	$117.05	$117.05	$117.10
Purchase #3	$51.27	8.582%	$55.67	$55.67	$55.65	$55.70
Purchase #4	$70.34	3.444%	$72.7625	$72.76	$72.75	$72.80
Purchase #5	$40.92	8.436%	$44.372	$44.37	$44.35	$44.40
Purchase #6	$36.30	7.673%	$39.0853	$39.09	$39.10	$39.10
Purchase #7	$113.52	5.514%	$119.7795	$119.78	$119.80	$119.80
7 purchase totals =	$494.85		$532.4578	$532.45	$532.45	$532.60