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	$172.89	8.290%	$187.2226	$187.22	$187.20	$187.20
Purchase #2	$103.67	4.321%	$108.1496	$108.15	$108.15	$108.10
Purchase #3	$174.56	7.524%	$187.6939	$187.69	$187.70	$187.70
Purchase #4	$90.61	10.808%	$100.4031	$100.40	$100.40	$100.40
Purchase #5	$144.93	7.787%	$156.2157	$156.22	$156.20	$156.20
Purchase #6	$89.71	4.809%	$94.0242	$94.02	$94.00	$94.00
Purchase #7	$128.53	7.452%	$138.1081	$138.11	$138.10	$138.10
7 purchase totals =	$904.90		$971.8172	$971.81	$971.75	$971.70