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	$71.57	7.198%	$76.7216	$76.72	$76.70	$76.70
Purchase #2	$6.51	4.321%	$6.7913	$6.79	$6.80	$6.80
Purchase #3	$41.72	12.494%	$46.9325	$46.93	$46.95	$46.90
Purchase #4	$209.71	11.497%	$233.8204	$233.82	$233.80	$233.80
Purchase #5	$173.33	9.426%	$189.6681	$189.67	$189.65	$189.70
Purchase #6	$39.57	12.390%	$44.4727	$44.47	$44.45	$44.50
Purchase #7	$84.91	5.401%	$89.496	$89.50	$89.50	$89.50
7 purchase totals =	$627.32		$687.9026	$687.90	$687.85	$687.90