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	$45.64	9.253%	$49.8631	$49.86	$49.85	$49.90
Purchase #2	$237.52	11.248%	$264.2362	$264.24	$264.25	$264.20
Purchase #3	$82.78	3.747%	$85.8818	$85.88	$85.90	$85.90
Purchase #4	$115.53	8.112%	$124.9018	$124.90	$124.90	$124.90
Purchase #5	$136.65	6.510%	$145.5459	$145.55	$145.55	$145.50
Purchase #6	$87.93	9.759%	$96.5111	$96.51	$96.50	$96.50
Purchase #7	$19.63	6.152%	$20.8376	$20.84	$20.85	$20.80
7 purchase totals =	$725.68		$787.7775	$787.78	$787.80	$787.70