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	$48.27	6.799%	$51.5519	$51.55	$51.55	$51.60
Purchase #2	$135.81	3.372%	$140.3895	$140.39	$140.40	$140.40
Purchase #3	$49.44	10.669%	$54.7148	$54.71	$54.70	$54.70
Purchase #4	$157.54	10.643%	$174.307	$174.31	$174.30	$174.30
Purchase #5	$152.82	12.516%	$171.947	$171.95	$171.95	$171.90
Purchase #6	$222.66	7.637%	$239.6645	$239.66	$239.65	$239.70
Purchase #7	$131.30	10.813%	$145.4975	$145.50	$145.50	$145.50
7 purchase totals =	$897.84		$978.0722	$978.07	$978.05	$978.10