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	$36.90	4.359%	$38.5085	$38.51	$38.50	$38.50
Purchase #2	$180.80	3.120%	$186.441	$186.44	$186.45	$186.40
Purchase #3	$247.94	6.697%	$264.5445	$264.54	$264.55	$264.50
Purchase #4	$137.33	13.188%	$155.4411	$155.44	$155.45	$155.40
Purchase #5	$35.33	8.417%	$38.3037	$38.30	$38.30	$38.30
Purchase #6	$131.76	5.180%	$138.5852	$138.59	$138.60	$138.60
Purchase #7	$189.36	10.677%	$209.578	$209.58	$209.60	$209.60
7 purchase totals =	$959.42		$1,031.4020	$1,031.40	$1,031.45	$1,031.30