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	$79.83	11.368%	$88.9051	$88.91	$88.90	$88.90
Purchase #2	$114.98	3.866%	$119.4251	$119.43	$119.45	$119.40
Purchase #3	$42.29	7.720%	$45.5548	$45.55	$45.55	$45.60
Purchase #4	$103.77	12.425%	$116.6634	$116.66	$116.65	$116.70
Purchase #5	$92.84	4.331%	$96.8609	$96.86	$96.85	$96.90
Purchase #6	$162.70	3.417%	$168.2595	$168.26	$168.25	$168.30
Purchase #7	$237.48	11.802%	$265.5074	$265.51	$265.50	$265.50
7 purchase totals =	$833.89		$901.1762	$901.18	$901.15	$901.30