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	$249.31	8.424%	$270.3119	$270.31	$270.30	$270.30
Purchase #2	$110.59	4.699%	$115.7866	$115.79	$115.80	$115.80
Purchase #3	$123.34	3.112%	$127.1783	$127.18	$127.20	$127.20
Purchase #4	$17.60	4.151%	$18.3306	$18.33	$18.35	$18.30
Purchase #5	$92.92	11.380%	$103.4943	$103.49	$103.50	$103.50
Purchase #6	$23.78	7.252%	$25.5045	$25.50	$25.50	$25.50
Purchase #7	$227.94	9.209%	$248.931	$248.93	$248.95	$248.90
7 purchase totals =	$845.48		$909.5372	$909.53	$909.60	$909.50