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	$201.58	5.674%	$213.0176	$213.02	$213.00	$213.00
Purchase #2	$48.67	9.171%	$53.1335	$53.13	$53.15	$53.10
Purchase #3	$231.36	11.871%	$258.8247	$258.82	$258.80	$258.80
Purchase #4	$93.40	11.614%	$104.2475	$104.25	$104.25	$104.20
Purchase #5	$82.88	7.481%	$89.0803	$89.08	$89.10	$89.10
Purchase #6	$61.67	12.840%	$69.5884	$69.59	$69.60	$69.60
Purchase #7	$40.93	11.579%	$45.6693	$45.67	$45.65	$45.70
7 purchase totals =	$760.49		$833.5613	$833.56	$833.55	$833.50