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	$223.89	7.401%	$240.4601	$240.46	$240.45	$240.50
Purchase #2	$168.96	5.831%	$178.8121	$178.81	$178.80	$178.80
Purchase #3	$92.34	5.510%	$97.4279	$97.43	$97.45	$97.40
Purchase #4	$249.48	10.471%	$275.6031	$275.60	$275.60	$275.60
Purchase #5	$113.60	9.872%	$124.8146	$124.81	$124.80	$124.80
Purchase #6	$219.67	12.147%	$246.3533	$246.35	$246.35	$246.40
Purchase #7	$123.86	6.146%	$131.4724	$131.47	$131.45	$131.50
7 purchase totals =	$1,191.80		$1,294.9435	$1,294.93	$1,294.90	$1,295.00