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	$145.76	6.768%	$155.625	$155.63	$155.65	$155.60
Purchase #2	$15.83	13.593%	$17.9818	$17.98	$18.00	$18.00
Purchase #3	$161.73	4.274%	$168.6423	$168.64	$168.65	$168.60
Purchase #4	$41.30	4.829%	$43.2944	$43.29	$43.30	$43.30
Purchase #5	$170.33	9.359%	$186.2712	$186.27	$186.25	$186.30
Purchase #6	$203.62	11.562%	$227.1625	$227.16	$227.15	$227.20
Purchase #7	$114.82	3.171%	$118.4609	$118.46	$118.45	$118.50
7 purchase totals =	$853.39		$917.4381	$917.43	$917.45	$917.50