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	$141.79	6.163%	$150.5285	$150.53	$150.55	$150.50
Purchase #2	$129.94	9.571%	$142.3766	$142.38	$142.40	$142.40
Purchase #3	$84.61	8.555%	$91.8484	$91.85	$91.85	$91.80
Purchase #4	$161.30	6.789%	$172.2507	$172.25	$172.25	$172.30
Purchase #5	$44.61	13.167%	$50.4838	$50.48	$50.50	$50.50
Purchase #6	$210.44	8.424%	$228.1675	$228.17	$228.15	$228.20
Purchase #7	$24.73	3.407%	$25.5726	$25.57	$25.55	$25.60
7 purchase totals =	$797.42		$861.2281	$861.23	$861.25	$861.30