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	$30.41	8.114%	$32.8775	$32.88	$32.90	$32.90
Purchase #2	$67.88	13.711%	$77.187	$77.19	$77.20	$77.20
Purchase #3	$143.95	3.462%	$148.9335	$148.93	$148.95	$148.90
Purchase #4	$98.88	13.120%	$111.8531	$111.85	$111.85	$111.90
Purchase #5	$17.56	10.473%	$19.3991	$19.40	$19.40	$19.40
Purchase #6	$156.36	8.609%	$169.821	$169.82	$169.80	$169.80
Purchase #7	$210.68	13.816%	$239.7875	$239.79	$239.80	$239.80
7 purchase totals =	$725.72		$799.8587	$799.86	$799.90	$799.90