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	$90.59	12.498%	$101.9119	$101.91	$101.90	$101.90
Purchase #2	$246.95	10.681%	$273.3267	$273.33	$273.35	$273.30
Purchase #3	$225.87	5.644%	$238.6181	$238.62	$238.60	$238.60
Purchase #4	$7.39	3.361%	$7.6384	$7.64	$7.65	$7.60
Purchase #5	$67.58	5.260%	$71.1347	$71.13	$71.15	$71.10
Purchase #6	$99.77	12.318%	$112.0597	$112.06	$112.05	$112.10
Purchase #7	$38.30	7.341%	$41.1116	$41.11	$41.10	$41.10
7 purchase totals =	$776.45		$845.8011	$845.80	$845.80	$845.70