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	$164.84	8.810%	$179.3624	$179.36	$179.35	$179.40
Purchase #2	$84.30	7.176%	$90.3494	$90.35	$90.35	$90.30
Purchase #3	$133.46	9.233%	$145.7824	$145.78	$145.80	$145.80
Purchase #4	$146.83	4.130%	$152.8941	$152.89	$152.90	$152.90
Purchase #5	$243.62	10.801%	$269.9334	$269.93	$269.95	$269.90
Purchase #6	$89.60	7.200%	$96.0512	$96.05	$96.05	$96.10
Purchase #7	$78.52	9.499%	$85.9786	$85.98	$86.00	$86.00
7 purchase totals =	$941.17		$1,020.3515	$1,020.34	$1,020.40	$1,020.40