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	$110.47	11.579%	$123.2613	$123.26	$123.25	$123.30
Purchase #2	$148.60	5.507%	$156.7834	$156.78	$156.80	$156.80
Purchase #3	$247.81	9.600%	$271.5998	$271.60	$271.60	$271.60
Purchase #4	$82.53	9.190%	$90.1145	$90.11	$90.10	$90.10
Purchase #5	$185.30	9.632%	$203.1481	$203.15	$203.15	$203.10
Purchase #6	$14.28	13.815%	$16.2528	$16.25	$16.25	$16.30
Purchase #7	$105.48	13.516%	$119.7367	$119.74	$119.75	$119.70
7 purchase totals =	$894.47		$980.8966	$980.89	$980.90	$980.90