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	$82.66	9.156%	$90.2283	$90.23	$90.25	$90.20
Purchase #2	$202.50	8.746%	$220.2107	$220.21	$220.20	$220.20
Purchase #3	$149.94	6.803%	$160.1404	$160.14	$160.15	$160.10
Purchase #4	$119.29	4.445%	$124.5924	$124.59	$124.60	$124.60
Purchase #5	$86.80	11.250%	$96.565	$96.57	$96.55	$96.60
Purchase #6	$118.52	11.220%	$131.8179	$131.82	$131.80	$131.80
Purchase #7	$20.61	4.222%	$21.4802	$21.48	$21.50	$21.50
7 purchase totals =	$780.32		$845.0349	$845.04	$845.05	$845.00