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	$78.40	13.544%	$89.0185	$89.02	$89.00	$89.00
Purchase #2	$104.73	3.157%	$108.0363	$108.04	$108.05	$108.00
Purchase #3	$226.26	3.811%	$234.8828	$234.88	$234.90	$234.90
Purchase #4	$108.76	4.172%	$113.2975	$113.30	$113.30	$113.30
Purchase #5	$77.95	12.429%	$87.6384	$87.64	$87.65	$87.60
Purchase #6	$174.64	12.524%	$196.5119	$196.51	$196.50	$196.50
Purchase #7	$124.56	5.721%	$131.6861	$131.69	$131.70	$131.70
7 purchase totals =	$895.30		$961.0715	$961.08	$961.10	$961.00