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	$39.31	11.363%	$43.7768	$43.78	$43.80	$43.80
Purchase #2	$61.51	9.762%	$67.5146	$67.51	$67.50	$67.50
Purchase #3	$200.46	12.163%	$224.8419	$224.84	$224.85	$224.80
Purchase #4	$30.47	6.834%	$32.5523	$32.55	$32.55	$32.60
Purchase #5	$166.55	7.287%	$178.6865	$178.69	$178.70	$178.70
Purchase #6	$55.28	11.508%	$61.6416	$61.64	$61.65	$61.60
Purchase #7	$228.63	6.710%	$243.9711	$243.97	$243.95	$244.00
7 purchase totals =	$782.21		$852.9848	$852.98	$853.00	$853.00