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	$128.71	6.337%	$136.8664	$136.87	$136.85	$136.90
Purchase #2	$232.45	7.714%	$250.3812	$250.38	$250.40	$250.40
Purchase #3	$249.35	8.376%	$270.2356	$270.24	$270.25	$270.20
Purchase #4	$39.95	8.594%	$43.3833	$43.38	$43.40	$43.40
Purchase #5	$156.49	7.798%	$168.6931	$168.69	$168.70	$168.70
Purchase #6	$7.54	13.164%	$8.5326	$8.53	$8.55	$8.50
Purchase #7	$83.85	6.476%	$89.2801	$89.28	$89.30	$89.30
7 purchase totals =	$898.34		$967.3723	$967.37	$967.45	$967.40