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	$189.80	8.263%	$205.4832	$205.48	$205.50	$205.50
Purchase #2	$166.89	3.172%	$172.1838	$172.18	$172.20	$172.20
Purchase #3	$249.31	7.853%	$268.8883	$268.89	$268.90	$268.90
Purchase #4	$92.72	4.781%	$97.1529	$97.15	$97.15	$97.20
Purchase #5	$131.30	3.550%	$135.9612	$135.96	$135.95	$136.00
Purchase #6	$115.39	7.612%	$124.1735	$124.17	$124.15	$124.20
Purchase #7	$90.63	6.393%	$96.424	$96.42	$96.40	$96.40
7 purchase totals =	$1,036.04		$1,100.2669	$1,100.25	$1,100.25	$1,100.40