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	$76.53	9.377%	$83.7062	$83.71	$83.70	$83.70
Purchase #2	$80.78	11.220%	$89.8435	$89.84	$89.85	$89.80
Purchase #3	$84.41	12.344%	$94.8296	$94.83	$94.85	$94.80
Purchase #4	$28.90	9.719%	$31.7088	$31.71	$31.70	$31.70
Purchase #5	$229.50	6.533%	$244.4932	$244.49	$244.50	$244.50
Purchase #6	$74.86	8.847%	$81.4829	$81.48	$81.50	$81.50
Purchase #7	$205.94	11.830%	$230.3027	$230.30	$230.30	$230.30
7 purchase totals =	$780.92		$856.3669	$856.36	$856.40	$856.30