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	$248.52	3.260%	$256.6218	$256.62	$256.60	$256.60
Purchase #2	$82.49	5.372%	$86.9214	$86.92	$86.90	$86.90
Purchase #3	$130.88	13.500%	$148.5488	$148.55	$148.55	$148.50
Purchase #4	$64.84	10.431%	$71.6035	$71.60	$71.60	$71.60
Purchase #5	$35.61	11.224%	$39.6069	$39.61	$39.60	$39.60
Purchase #6	$72.86	10.783%	$80.7165	$80.72	$80.70	$80.70
Purchase #7	$73.35	13.573%	$83.3058	$83.31	$83.30	$83.30
7 purchase totals =	$708.55		$767.3247	$767.33	$767.25	$767.20