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	$35.35	12.456%	$39.7532	$39.75	$39.75	$39.80
Purchase #2	$109.89	12.423%	$123.5416	$123.54	$123.55	$123.50
Purchase #3	$64.35	12.371%	$72.3107	$72.31	$72.30	$72.30
Purchase #4	$159.71	7.124%	$171.0877	$171.09	$171.10	$171.10
Purchase #5	$213.74	11.464%	$238.2432	$238.24	$238.25	$238.20
Purchase #6	$196.85	11.162%	$218.8224	$218.82	$218.80	$218.80
Purchase #7	$156.88	5.585%	$165.6417	$165.64	$165.65	$165.60
7 purchase totals =	$936.77		$1,029.4005	$1,029.39	$1,029.40	$1,029.30