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	$101.59	3.482%	$105.1274	$105.13	$105.15	$105.10
Purchase #2	$81.63	6.317%	$86.7866	$86.79	$86.80	$86.80
Purchase #3	$138.51	3.221%	$142.9714	$142.97	$142.95	$143.00
Purchase #4	$156.31	9.340%	$170.9094	$170.91	$170.90	$170.90
Purchase #5	$69.38	4.334%	$72.3869	$72.39	$72.40	$72.40
Purchase #6	$160.28	3.171%	$165.3625	$165.36	$165.35	$165.40
Purchase #7	$82.60	6.337%	$87.8344	$87.83	$87.85	$87.80
7 purchase totals =	$790.30		$831.3786	$831.38	$831.40	$831.40