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	$55.61	3.552%	$57.5853	$57.59	$57.60	$57.60
Purchase #2	$218.73	10.438%	$241.561	$241.56	$241.55	$241.60
Purchase #3	$203.53	4.713%	$213.1224	$213.12	$213.10	$213.10
Purchase #4	$115.26	7.443%	$123.8388	$123.84	$123.85	$123.80
Purchase #5	$99.86	13.854%	$113.6946	$113.69	$113.70	$113.70
Purchase #6	$78.31	4.355%	$81.7204	$81.72	$81.70	$81.70
Purchase #7	$55.94	6.158%	$59.3848	$59.38	$59.40	$59.40
7 purchase totals =	$827.24		$890.9073	$890.90	$890.90	$890.90