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	$79.38	12.749%	$89.5002	$89.50	$89.50	$89.50
Purchase #2	$178.63	3.498%	$184.8785	$184.88	$184.90	$184.90
Purchase #3	$34.45	8.790%	$37.4782	$37.48	$37.50	$37.50
Purchase #4	$5.75	13.443%	$6.523	$6.52	$6.50	$6.50
Purchase #5	$24.45	7.324%	$26.2407	$26.24	$26.25	$26.20
Purchase #6	$81.94	5.576%	$86.509	$86.51	$86.50	$86.50
Purchase #7	$109.73	8.316%	$118.8551	$118.86	$118.85	$118.90
7 purchase totals =	$514.33		$549.9847	$549.99	$550.00	$550.00