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	$53.32	8.199%	$57.6917	$57.69	$57.70	$57.70
Purchase #2	$78.51	3.548%	$81.2955	$81.30	$81.30	$81.30
Purchase #3	$19.59	11.405%	$21.8242	$21.82	$21.80	$21.80
Purchase #4	$111.27	12.153%	$124.7926	$124.79	$124.80	$124.80
Purchase #5	$69.36	3.716%	$71.9374	$71.94	$71.95	$71.90
Purchase #6	$220.57	6.720%	$235.3923	$235.39	$235.40	$235.40
Purchase #7	$242.72	9.135%	$264.8925	$264.89	$264.90	$264.90
7 purchase totals =	$795.34		$857.8262	$857.82	$857.85	$857.80