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	$124.88	10.437%	$137.9137	$137.91	$137.90	$137.90
Purchase #2	$194.63	7.841%	$209.8909	$209.89	$209.90	$209.90
Purchase #3	$44.69	10.334%	$49.3083	$49.31	$49.30	$49.30
Purchase #4	$73.73	6.848%	$78.779	$78.78	$78.80	$78.80
Purchase #5	$48.91	9.838%	$53.7218	$53.72	$53.70	$53.70
Purchase #6	$217.29	3.677%	$225.2798	$225.28	$225.30	$225.30
Purchase #7	$200.69	11.585%	$223.9399	$223.94	$223.95	$223.90
7 purchase totals =	$904.82		$978.8334	$978.83	$978.85	$978.80