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	$33.33	11.568%	$37.1856	$37.19	$37.20	$37.20
Purchase #2	$231.29	3.259%	$238.8277	$238.83	$238.85	$238.80
Purchase #3	$166.51	11.678%	$185.955	$185.96	$185.95	$186.00
Purchase #4	$181.45	10.729%	$200.9178	$200.92	$200.90	$200.90
Purchase #5	$90.90	4.817%	$95.2787	$95.28	$95.30	$95.30
Purchase #6	$130.31	7.357%	$139.8969	$139.90	$139.90	$139.90
Purchase #7	$217.50	11.517%	$242.5495	$242.55	$242.55	$242.50
7 purchase totals =	$1,051.29		$1,140.6112	$1,140.63	$1,140.65	$1,140.60