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	$81.44	11.221%	$90.5784	$90.58	$90.60	$90.60
Purchase #2	$86.97	13.246%	$98.49	$98.49	$98.50	$98.50
Purchase #3	$210.88	5.755%	$223.0161	$223.02	$223.00	$223.00
Purchase #4	$150.57	12.601%	$169.5433	$169.54	$169.55	$169.50
Purchase #5	$232.45	5.205%	$244.549	$244.55	$244.55	$244.50
Purchase #6	$88.67	13.310%	$100.472	$100.47	$100.45	$100.50
Purchase #7	$20.45	6.799%	$21.8404	$21.84	$21.85	$21.80
7 purchase totals =	$871.43		$948.4892	$948.49	$948.50	$948.40