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	$200.38	12.332%	$225.0909	$225.09	$225.10	$225.10
Purchase #2	$28.47	11.579%	$31.7665	$31.77	$31.75	$31.80
Purchase #3	$225.76	6.667%	$240.8114	$240.81	$240.80	$240.80
Purchase #4	$79.69	10.267%	$87.8718	$87.87	$87.85	$87.90
Purchase #5	$62.33	13.740%	$70.8941	$70.89	$70.90	$70.90
Purchase #6	$234.75	12.822%	$264.8496	$264.85	$264.85	$264.80
Purchase #7	$37.95	13.296%	$42.9958	$43.00	$43.00	$43.00
7 purchase totals =	$869.33		$964.2801	$964.28	$964.25	$964.30