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	$45.68	13.640%	$51.9108	$51.91	$51.90	$51.90
Purchase #2	$85.99	5.512%	$90.7298	$90.73	$90.75	$90.70
Purchase #3	$46.84	6.865%	$50.0556	$50.06	$50.05	$50.10
Purchase #4	$80.82	7.132%	$86.5841	$86.58	$86.60	$86.60
Purchase #5	$206.57	12.168%	$231.7054	$231.71	$231.70	$231.70
Purchase #6	$86.54	9.176%	$94.4809	$94.48	$94.50	$94.50
Purchase #7	$210.95	3.774%	$218.9113	$218.91	$218.90	$218.90
7 purchase totals =	$763.39		$824.3779	$824.38	$824.40	$824.40