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	$249.76	10.669%	$276.4069	$276.41	$276.40	$276.40
Purchase #2	$234.46	6.581%	$249.8898	$249.89	$249.90	$249.90
Purchase #3	$215.92	10.240%	$238.0302	$238.03	$238.05	$238.00
Purchase #4	$35.74	13.457%	$40.5495	$40.55	$40.55	$40.50
Purchase #5	$102.64	12.862%	$115.8416	$115.84	$115.85	$115.80
Purchase #6	$67.60	7.798%	$72.8714	$72.87	$72.85	$72.90
Purchase #7	$135.86	13.193%	$153.784	$153.78	$153.80	$153.80
7 purchase totals =	$1,041.98		$1,147.3734	$1,147.37	$1,147.40	$1,147.30