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	$62.97	13.163%	$71.2587	$71.26	$71.25	$71.30
Purchase #2	$202.47	7.799%	$218.2606	$218.26	$218.25	$218.30
Purchase #3	$84.66	6.201%	$89.9098	$89.91	$89.90	$89.90
Purchase #4	$38.39	10.811%	$42.5403	$42.54	$42.55	$42.50
Purchase #5	$122.64	12.308%	$137.7345	$137.73	$137.75	$137.70
Purchase #6	$174.56	13.454%	$198.0453	$198.05	$198.05	$198.00
Purchase #7	$211.54	5.414%	$222.9928	$222.99	$223.00	$223.00
7 purchase totals =	$897.23		$980.7420	$980.74	$980.75	$980.70