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	$68.55	7.404%	$73.6254	$73.63	$73.65	$73.60
Purchase #2	$42.36	4.417%	$44.231	$44.23	$44.25	$44.20
Purchase #3	$115.46	13.712%	$131.2919	$131.29	$131.30	$131.30
Purchase #4	$148.33	9.405%	$162.2804	$162.28	$162.30	$162.30
Purchase #5	$77.81	7.280%	$83.4746	$83.47	$83.45	$83.50
Purchase #6	$74.56	4.470%	$77.8928	$77.89	$77.90	$77.90
Purchase #7	$92.36	3.810%	$95.8789	$95.88	$95.90	$95.90
7 purchase totals =	$619.43		$668.6750	$668.67	$668.75	$668.70