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	$87.47	13.201%	$99.0169	$99.02	$99.00	$99.00
Purchase #2	$87.72	10.241%	$96.7034	$96.70	$96.70	$96.70
Purchase #3	$113.91	9.216%	$124.4079	$124.41	$124.40	$124.40
Purchase #4	$67.79	6.764%	$72.3753	$72.38	$72.40	$72.40
Purchase #5	$38.71	4.156%	$40.3188	$40.32	$40.30	$40.30
Purchase #6	$121.52	13.390%	$137.7915	$137.79	$137.80	$137.80
Purchase #7	$211.53	12.523%	$238.0199	$238.02	$238.00	$238.00
7 purchase totals =	$728.65		$808.6337	$808.64	$808.60	$808.60