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	$103.35	6.318%	$109.8797	$109.88	$109.90	$109.90
Purchase #2	$35.48	10.356%	$39.1543	$39.15	$39.15	$39.20
Purchase #3	$234.53	8.466%	$254.3853	$254.39	$254.40	$254.40
Purchase #4	$126.98	8.623%	$137.9295	$137.93	$137.95	$137.90
Purchase #5	$132.77	6.815%	$141.8183	$141.82	$141.80	$141.80
Purchase #6	$190.33	12.188%	$213.5274	$213.53	$213.55	$213.50
Purchase #7	$159.54	12.697%	$179.7968	$179.80	$179.80	$179.80
7 purchase totals =	$982.98		$1,076.4913	$1,076.50	$1,076.55	$1,076.50