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	$139.37	7.871%	$150.3398	$150.34	$150.35	$150.30
Purchase #2	$28.58	4.348%	$29.8227	$29.82	$29.80	$29.80
Purchase #3	$209.97	9.140%	$229.1613	$229.16	$229.15	$229.20
Purchase #4	$187.77	13.189%	$212.535	$212.54	$212.55	$212.50
Purchase #5	$230.86	12.359%	$259.392	$259.39	$259.40	$259.40
Purchase #6	$200.48	10.673%	$221.8772	$221.88	$221.90	$221.90
Purchase #7	$143.34	5.272%	$150.8969	$150.90	$150.90	$150.90
7 purchase totals =	$1,140.37		$1,254.0249	$1,254.03	$1,254.05	$1,254.00