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	$55.37	7.544%	$59.5471	$59.55	$59.55	$59.50
Purchase #2	$141.42	6.140%	$150.1032	$150.10	$150.10	$150.10
Purchase #3	$175.60	6.386%	$186.8138	$186.81	$186.80	$186.80
Purchase #4	$134.74	10.233%	$148.5279	$148.53	$148.55	$148.50
Purchase #5	$38.45	10.181%	$42.3646	$42.36	$42.35	$42.40
Purchase #6	$212.72	13.757%	$241.9839	$241.98	$242.00	$242.00
Purchase #7	$232.34	5.431%	$244.9584	$244.96	$244.95	$245.00
7 purchase totals =	$990.64		$1,074.2989	$1,074.29	$1,074.30	$1,074.30