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	$81.86	7.871%	$88.3032	$88.30	$88.30	$88.30
Purchase #2	$127.40	5.657%	$134.607	$134.61	$134.60	$134.60
Purchase #3	$119.48	11.762%	$133.5332	$133.53	$133.55	$133.50
Purchase #4	$98.80	12.468%	$111.1184	$111.12	$111.10	$111.10
Purchase #5	$148.68	10.703%	$164.5932	$164.59	$164.60	$164.60
Purchase #6	$196.73	8.221%	$212.9032	$212.90	$212.90	$212.90
Purchase #7	$155.32	6.253%	$165.0322	$165.03	$165.05	$165.00
7 purchase totals =	$928.27		$1,010.0904	$1,010.08	$1,010.10	$1,010.00