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	$62.88	12.558%	$70.7765	$70.78	$70.80	$70.80
Purchase #2	$83.86	7.685%	$90.3046	$90.30	$90.30	$90.30
Purchase #3	$98.38	12.791%	$110.9638	$110.96	$110.95	$111.00
Purchase #4	$184.34	13.162%	$208.6028	$208.60	$208.60	$208.60
Purchase #5	$150.52	7.164%	$161.3033	$161.30	$161.30	$161.30
Purchase #6	$6.46	12.821%	$7.2882	$7.29	$7.30	$7.30
Purchase #7	$24.50	7.221%	$26.2691	$26.27	$26.25	$26.30
7 purchase totals =	$610.94		$675.5083	$675.50	$675.50	$675.60