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	$245.83	4.354%	$256.5334	$256.53	$256.55	$256.50
Purchase #2	$204.91	4.659%	$214.4568	$214.46	$214.45	$214.50
Purchase #3	$198.84	6.546%	$211.8561	$211.86	$211.85	$211.90
Purchase #4	$35.82	12.629%	$40.3437	$40.34	$40.35	$40.30
Purchase #5	$135.49	6.512%	$144.3131	$144.31	$144.30	$144.30
Purchase #6	$79.91	11.637%	$89.2091	$89.21	$89.20	$89.20
Purchase #7	$131.75	8.426%	$142.8513	$142.85	$142.85	$142.90
7 purchase totals =	$1,032.55		$1,099.5635	$1,099.56	$1,099.55	$1,099.60