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	$44.31	7.589%	$47.6727	$47.67	$47.65	$47.70
Purchase #2	$91.84	5.471%	$96.8646	$96.86	$96.85	$96.90
Purchase #3	$56.47	5.386%	$59.5115	$59.51	$59.50	$59.50
Purchase #4	$33.64	11.655%	$37.5607	$37.56	$37.55	$37.60
Purchase #5	$93.76	10.375%	$103.4876	$103.49	$103.50	$103.50
Purchase #6	$227.67	12.452%	$256.0195	$256.02	$256.00	$256.00
Purchase #7	$225.53	5.416%	$237.7447	$237.74	$237.75	$237.70
7 purchase totals =	$773.22		$838.8613	$838.85	$838.80	$838.90