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	$5.70	10.118%	$6.2767	$6.28	$6.30	$6.30
Purchase #2	$78.30	7.140%	$83.8906	$83.89	$83.90	$83.90
Purchase #3	$157.28	3.343%	$162.5379	$162.54	$162.55	$162.50
Purchase #4	$123.32	11.562%	$137.5783	$137.58	$137.60	$137.60
Purchase #5	$48.68	13.721%	$55.3594	$55.36	$55.35	$55.40
Purchase #6	$229.93	7.374%	$246.885	$246.89	$246.90	$246.90
Purchase #7	$191.35	12.726%	$215.7012	$215.70	$215.70	$215.70
7 purchase totals =	$834.56		$908.2291	$908.24	$908.30	$908.30