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	$52.45	4.874%	$55.0064	$55.01	$55.00	$55.00
Purchase #2	$92.45	7.131%	$99.0426	$99.04	$99.05	$99.00
Purchase #3	$73.61	12.269%	$82.6412	$82.64	$82.65	$82.60
Purchase #4	$219.64	12.599%	$247.3124	$247.31	$247.30	$247.30
Purchase #5	$180.89	13.127%	$204.6354	$204.64	$204.65	$204.60
Purchase #6	$42.43	12.698%	$47.8178	$47.82	$47.80	$47.80
Purchase #7	$28.31	3.799%	$29.3855	$29.39	$29.40	$29.40
7 purchase totals =	$689.78		$765.8413	$765.85	$765.85	$765.70