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	$136.99	3.462%	$141.7326	$141.73	$141.75	$141.70
Purchase #2	$9.79	10.821%	$10.8494	$10.85	$10.85	$10.80
Purchase #3	$169.27	6.404%	$180.1101	$180.11	$180.10	$180.10
Purchase #4	$162.34	7.234%	$174.0837	$174.08	$174.10	$174.10
Purchase #5	$32.59	11.653%	$36.3877	$36.39	$36.40	$36.40
Purchase #6	$186.92	7.279%	$200.5259	$200.53	$200.55	$200.50
Purchase #7	$206.40	13.725%	$234.7284	$234.73	$234.75	$234.70
7 purchase totals =	$904.30		$978.4178	$978.42	$978.50	$978.30