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	$127.81	7.373%	$137.2334	$137.23	$137.25	$137.20
Purchase #2	$130.57	12.691%	$147.1406	$147.14	$147.15	$147.10
Purchase #3	$96.79	4.281%	$100.9336	$100.93	$100.95	$100.90
Purchase #4	$75.33	9.241%	$82.2912	$82.29	$82.30	$82.30
Purchase #5	$137.28	5.138%	$144.3334	$144.33	$144.35	$144.30
Purchase #6	$110.82	7.524%	$119.1581	$119.16	$119.15	$119.20
Purchase #7	$195.71	12.808%	$220.7765	$220.78	$220.80	$220.80
7 purchase totals =	$874.31		$951.8668	$951.86	$951.95	$951.80