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	$184.79	5.805%	$195.5171	$195.52	$195.50	$195.50
Purchase #2	$38.62	10.589%	$42.7095	$42.71	$42.70	$42.70
Purchase #3	$94.63	10.654%	$104.7119	$104.71	$104.70	$104.70
Purchase #4	$227.59	13.672%	$258.7061	$258.71	$258.70	$258.70
Purchase #5	$92.81	13.722%	$105.5454	$105.55	$105.55	$105.50
Purchase #6	$41.40	9.540%	$45.3496	$45.35	$45.35	$45.30
Purchase #7	$88.61	12.750%	$99.9078	$99.91	$99.90	$99.90
7 purchase totals =	$768.45		$852.4474	$852.46	$852.40	$852.30