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	$179.76	5.330%	$189.3412	$189.34	$189.35	$189.30
Purchase #2	$46.30	11.392%	$51.5745	$51.57	$51.55	$51.60
Purchase #3	$36.56	9.569%	$40.0584	$40.06	$40.05	$40.10
Purchase #4	$149.48	11.426%	$166.5596	$166.56	$166.55	$166.60
Purchase #5	$50.31	13.605%	$57.1547	$57.15	$57.15	$57.20
Purchase #6	$33.93	9.726%	$37.23	$37.23	$37.25	$37.20
Purchase #7	$53.82	10.216%	$59.3183	$59.32	$59.30	$59.30
7 purchase totals =	$550.16		$601.2367	$601.23	$601.20	$601.30