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	$7.77	8.515%	$8.4316	$8.43	$8.45	$8.40
Purchase #2	$67.75	7.677%	$72.9512	$72.95	$72.95	$73.00
Purchase #3	$237.52	13.781%	$270.2526	$270.25	$270.25	$270.30
Purchase #4	$74.99	8.872%	$81.6431	$81.64	$81.65	$81.60
Purchase #5	$64.75	9.867%	$71.1389	$71.14	$71.15	$71.10
Purchase #6	$110.53	11.458%	$123.1945	$123.19	$123.20	$123.20
Purchase #7	$37.45	7.553%	$40.2786	$40.28	$40.30	$40.30
7 purchase totals =	$600.76		$667.8905	$667.88	$667.95	$667.90