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	$79.94	8.703%	$86.8972	$86.90	$86.90	$86.90
Purchase #2	$170.98	11.432%	$190.5264	$190.53	$190.55	$190.50
Purchase #3	$7.68	3.655%	$7.9607	$7.96	$7.95	$8.00
Purchase #4	$51.29	10.306%	$56.5759	$56.58	$56.60	$56.60
Purchase #5	$75.46	9.327%	$82.4982	$82.50	$82.50	$82.50
Purchase #6	$90.30	6.726%	$96.3736	$96.37	$96.35	$96.40
Purchase #7	$139.57	4.158%	$145.3733	$145.37	$145.35	$145.40
7 purchase totals =	$615.22		$666.2053	$666.21	$666.20	$666.30