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	$130.36	7.303%	$139.8802	$139.88	$139.90	$139.90
Purchase #2	$120.66	8.176%	$130.5252	$130.53	$130.55	$130.50
Purchase #3	$168.34	6.336%	$179.006	$179.01	$179.00	$179.00
Purchase #4	$106.39	5.785%	$112.5447	$112.54	$112.55	$112.50
Purchase #5	$64.74	11.728%	$72.3327	$72.33	$72.35	$72.30
Purchase #6	$141.30	6.468%	$150.4393	$150.44	$150.45	$150.40
Purchase #7	$59.99	10.722%	$66.4221	$66.42	$66.40	$66.40
7 purchase totals =	$791.78		$851.1502	$851.15	$851.20	$851.00