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	$135.48	7.233%	$145.2793	$145.28	$145.30	$145.30
Purchase #2	$94.56	11.730%	$105.6519	$105.65	$105.65	$105.70
Purchase #3	$52.54	10.168%	$57.8823	$57.88	$57.90	$57.90
Purchase #4	$113.50	5.593%	$119.8481	$119.85	$119.85	$119.80
Purchase #5	$78.80	13.525%	$89.4577	$89.46	$89.45	$89.50
Purchase #6	$145.96	3.134%	$150.5344	$150.53	$150.55	$150.50
Purchase #7	$39.73	5.604%	$41.9565	$41.96	$41.95	$42.00
7 purchase totals =	$660.57		$710.6102	$710.61	$710.65	$710.70