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	$29.78	12.611%	$33.5356	$33.54	$33.55	$33.50
Purchase #2	$126.80	3.462%	$131.1898	$131.19	$131.20	$131.20
Purchase #3	$77.80	7.248%	$83.4389	$83.44	$83.45	$83.40
Purchase #4	$182.87	11.764%	$204.3828	$204.38	$204.40	$204.40
Purchase #5	$157.92	8.695%	$171.6511	$171.65	$171.65	$171.70
Purchase #6	$68.30	6.119%	$72.4793	$72.48	$72.50	$72.50
Purchase #7	$148.41	4.319%	$154.8198	$154.82	$154.80	$154.80
7 purchase totals =	$791.88		$851.4973	$851.50	$851.55	$851.50