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	$194.48	8.825%	$211.6429	$211.64	$211.65	$211.60
Purchase #2	$40.69	3.292%	$42.0295	$42.03	$42.05	$42.00
Purchase #3	$97.33	6.465%	$103.6224	$103.62	$103.60	$103.60
Purchase #4	$69.42	7.203%	$74.4203	$74.42	$74.40	$74.40
Purchase #5	$88.63	11.828%	$99.1132	$99.11	$99.10	$99.10
Purchase #6	$78.34	5.858%	$82.9292	$82.93	$82.95	$82.90
Purchase #7	$164.48	13.308%	$186.369	$186.37	$186.35	$186.40
7 purchase totals =	$733.37		$800.1265	$800.12	$800.10	$800.00