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	$206.58	7.619%	$222.3193	$222.32	$222.30	$222.30
Purchase #2	$98.89	11.270%	$110.0349	$110.03	$110.05	$110.00
Purchase #3	$53.81	11.261%	$59.8695	$59.87	$59.85	$59.90
Purchase #4	$221.37	13.684%	$251.6623	$251.66	$251.65	$251.70
Purchase #5	$39.41	6.600%	$42.0111	$42.01	$42.00	$42.00
Purchase #6	$96.54	12.206%	$108.3237	$108.32	$108.30	$108.30
Purchase #7	$137.87	12.151%	$154.6226	$154.62	$154.60	$154.60
7 purchase totals =	$854.47		$948.8434	$948.83	$948.75	$948.80