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	$38.78	9.732%	$42.5541	$42.55	$42.55	$42.60
Purchase #2	$214.47	5.220%	$225.6653	$225.67	$225.65	$225.70
Purchase #3	$62.44	13.574%	$70.9156	$70.92	$70.90	$70.90
Purchase #4	$208.92	4.614%	$218.5596	$218.56	$218.55	$218.60
Purchase #5	$45.41	6.521%	$48.3712	$48.37	$48.35	$48.40
Purchase #6	$113.48	13.405%	$128.692	$128.69	$128.70	$128.70
Purchase #7	$125.31	5.233%	$131.8675	$131.87	$131.85	$131.90
7 purchase totals =	$808.81		$866.6253	$866.63	$866.55	$866.80