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	$96.74	12.812%	$109.1343	$109.13	$109.15	$109.10
Purchase #2	$172.69	9.569%	$189.2147	$189.21	$189.20	$189.20
Purchase #3	$224.55	3.268%	$231.8883	$231.89	$231.90	$231.90
Purchase #4	$206.34	11.691%	$230.4632	$230.46	$230.45	$230.50
Purchase #5	$187.85	4.651%	$196.5869	$196.59	$196.60	$196.60
Purchase #6	$100.36	9.540%	$109.9343	$109.93	$109.95	$109.90
Purchase #7	$103.48	9.628%	$113.4431	$113.44	$113.45	$113.40
7 purchase totals =	$1,092.01		$1,180.6648	$1,180.65	$1,180.70	$1,180.60