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	$31.53	6.180%	$33.4786	$33.48	$33.50	$33.50
Purchase #2	$213.73	6.774%	$228.2081	$228.21	$228.20	$228.20
Purchase #3	$74.54	7.370%	$80.0336	$80.03	$80.05	$80.00
Purchase #4	$76.91	8.567%	$83.4989	$83.50	$83.50	$83.50
Purchase #5	$240.83	6.338%	$256.0938	$256.09	$256.10	$256.10
Purchase #6	$97.89	13.319%	$110.928	$110.93	$110.95	$110.90
Purchase #7	$82.76	7.766%	$89.1871	$89.19	$89.20	$89.20
7 purchase totals =	$818.19		$881.4281	$881.43	$881.50	$881.40