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	$78.38	9.186%	$85.58	$85.58	$85.60	$85.60
Purchase #2	$88.65	6.460%	$94.3768	$94.38	$94.40	$94.40
Purchase #3	$30.89	13.366%	$35.0188	$35.02	$35.00	$35.00
Purchase #4	$210.88	13.265%	$238.8532	$238.85	$238.85	$238.90
Purchase #5	$64.71	10.179%	$71.2968	$71.30	$71.30	$71.30
Purchase #6	$165.96	12.147%	$186.1192	$186.12	$186.10	$186.10
Purchase #7	$106.63	5.181%	$112.1545	$112.15	$112.15	$112.20
7 purchase totals =	$746.10		$823.3993	$823.40	$823.40	$823.50