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	$116.67	10.694%	$129.1467	$129.15	$129.15	$129.10
Purchase #2	$60.95	6.425%	$64.866	$64.87	$64.85	$64.90
Purchase #3	$219.33	4.558%	$229.3271	$229.33	$229.35	$229.30
Purchase #4	$166.96	13.691%	$189.8185	$189.82	$189.80	$189.80
Purchase #5	$103.45	5.776%	$109.4253	$109.43	$109.45	$109.40
Purchase #6	$73.43	7.479%	$78.9218	$78.92	$78.90	$78.90
Purchase #7	$7.63	3.833%	$7.9225	$7.92	$7.90	$7.90
7 purchase totals =	$748.42		$809.4279	$809.44	$809.40	$809.30