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	$55.61	7.283%	$59.6601	$59.66	$59.65	$59.70
Purchase #2	$222.99	7.700%	$240.1602	$240.16	$240.15	$240.20
Purchase #3	$104.47	12.343%	$117.3647	$117.36	$117.35	$117.40
Purchase #4	$19.37	12.794%	$21.8482	$21.85	$21.85	$21.80
Purchase #5	$43.64	6.429%	$46.4456	$46.45	$46.45	$46.40
Purchase #6	$55.27	3.129%	$56.9994	$57.00	$57.00	$57.00
Purchase #7	$55.34	3.743%	$57.4114	$57.41	$57.40	$57.40
7 purchase totals =	$556.69		$599.8896	$599.89	$599.85	$599.90