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	$110.25	9.136%	$120.3224	$120.32	$120.30	$120.30
Purchase #2	$67.82	5.576%	$71.6016	$71.60	$71.60	$71.60
Purchase #3	$68.87	13.135%	$77.9161	$77.92	$77.90	$77.90
Purchase #4	$94.31	12.256%	$105.8686	$105.87	$105.85	$105.90
Purchase #5	$245.45	7.535%	$263.9447	$263.94	$263.95	$263.90
Purchase #6	$71.99	13.732%	$81.8757	$81.88	$81.90	$81.90
Purchase #7	$249.79	12.854%	$281.898	$281.90	$281.90	$281.90
7 purchase totals =	$908.48		$1,003.4271	$1,003.43	$1,003.40	$1,003.40